July 25, 2021
The 5th chapter of Kristen O'Hara's book Sex as Nature Intended It began with a description of the gliding function that mutated into an embarrassingly gushing ode (emphasis in the original):
"Upon erection, the foreskin is transferred to the penile shaft and becomes part of the total shaft skin system. This results in a loose, movable shaft skin that provides the penis with a gentle gliding mechanism. During intercourse, the natural penis shaft actually glides within its own shaft skin covering. This minimizes friction to the vaginal walls and opening, and to the shaft skin itself, adding immeasurably to the comfort and pleasure of both partners...
Because of its special gliding function, the foreskin steals the show and plays the leading role during the performance of intercourse -- it's the SUPERSTAR of the sexual connection between a man and a woman. The interaction of the foreskin, penis shaft, and vaginal walls is passionate, sexual poetry in motion. The natural penis's coital 'glide-ride' gives both partners a thrilling lesson in sensual schooling they shall not soon forget. Ah, the unforgettable foreskin--that's what you are. How I do love thee and your unforgettable ways, daydreaming of you as I do..." 
Based on such excessive, almost worshipful adoration, one might expect to find conclusive proof that the foreskin provides a unique gliding function that makes vaginal intercourse with an uncircumcised man far superior to intercourse with a circumcised partner. Yet upon examination one would discover that the evidence, far from definitive, is illusory.
SEARCHING FOR EVIDENCE
A 1980 paper by SHAMUGAN LAKSHAMANAN and SATYA PARKASH  was reportedly the first source for a "gliding action" of the foreskin.  The researchers wrote that "The outer layer of the prepuce in common with the skin of the shaft of the penis glides freely in an to and fro fashion and has to be delicate and thin, as was observed in this study... The inner lining of the projecting tubular part has the structure of the outer layer and adds to the thin gliding skin when retracted." The researchers examined post-mortem specimens collected from 15 corpses (5 neonates, 5 boys under age seven, and 5 adult men.) This study cannot offer any proof that an uncircumcised penis glides more effectively or more pleasurably than a circumcised penis.
In his 1995 foreskin restoration book, JIM BIGELOW  wrote that the uncircumcised penis "thrusts in and out of its own skin sheath, until nearer the point of ejaculation when the glans expands further. This skin sheath acts as a kind of 'gliding mechanism' for the penis inside the vagina. As a result, the natural moisture provided by the female remains by and large within the vagina and is not dried up by the repeated thrusting of the male. This condition allows the female to be far more comfortable and to enjoy prolonged intercourse. Furthermore, since the foreskin hugs and stimulates the glans so perfectly, the male is more naturally stimulated throughout each phase of sexual arousal." Bigelow offered no evidence whatsoever to support these assertions. 
JOHN WARREN and BIGELOW  cited Bigelow's book to support their contention that "men who have restored their prepuce describe ... a discovery of the gliding action of slack skin on the shaft..." However the authors failed to cite any scientific studies on the possible effects of foreskin stretching on sexual function.
Colorado nurse GILLIAN LONGLEY, a NOCIRC state coordinator and a member of the Intact America Board of Health Professionals, explained the gliding function in a 2009 thesis (emphasis in the original):
"The double-layered fold of the foreskin acts as a rolling bearing during intercourse. Once the penis is inserted, friction from the vaginal walls holds the skin of the penis relatively stable, allowing the shaft of the penis to glide in and out of its own skin sheath with the motions of intercourse, instead of rubbing directly against the vaginal wall. The gliding, non-abrasive movement makes intercourse more comfortable for both partners (O'Hara & O'Hara, 1999; Scott, 1999). The mobility of the intact penile skin also plays a facilitating role in foreplay, masturbation, and insertion of the penis (Kim & Pang, 2007; Taves, 2002). One physician described the latter function in this way: Penetration in the circumcised man has been compared to thrusting the foot into a sock held open at the top, while, on the other hand, in the intact counterpart it has been likened to slipping the foot into a sock that has been previously rolled up (Morgan, 1965)." 
Let’s examine Longley's sources.
KRISTEN O'HARA and JEFFREY O'HARA  violated standard survey methodology throughout. The survey was conducted over a period of several years. Respondents were recruited via an ad placed in an anti-circumcision newsletter. Survey questions featured prejudicial terms and were structured to elicit responses favoring uncircumcised sex. Some questions were added or reworded during the survey period. 
STEVE SCOTT  wrote that circumcision hinders the capacity of a penis to enter and glide inside a vagina. "The unique ability of the penis to glide in and out of itself is dependent on a complete penile integument. The diminution of this integument limits or precludes the important role of penile skin mobility of sexual foreplay." Notwithstanding the lexiphanic language,  Scott failed to provide any citations or other evidence for his statement that a circumcised penis cannot glide inside a vagina.
DAISIK KIM and MYUNG-GEOL PANG  did not discuss the effect of circumcision on penile mobility. Their survey of men circumcised as adults cannot address the possible effects of infant circumcision on sexual function. Moreover, the researchers didn't distinguish between men circumcised to treat a medical condition and those circumcised for elective reasons. Men circumcised for medical reasons might have other factors that contribute to a decrease in sexual function.
DONALD TAVES  cut a quarter-size hole in the bottom of a Styrofoam cup to simulate a vaginal opening. He mounted the cup on a diet scale to measure the force that a circumcised man and an uncircumcised man would use to enter a partner's vagina. Taves penetrated the hole with his erect penis - alternately with his glans exposed, and with his foreskin covering the glans. He concluded that circumcised men use ten times greater force to enter a female partner than their uncircumcised peers. We're left speechless over the realization that this bizarre experiment is given any serious credibility. Longley's citation of Taves is a striking demonstration of the haphazard scholarship exhibited by anti-circumcision academics blind to their own confirmation bias. 
WILLIAM MORGAN  claimed that the uncircumcised penis penetrates smoothly and without friction, while the circumcised penis causes friction between the glans and the vagina. Morgan provided no evidence to support his assertion. And we're puzzled at the idea that friction is a bad thing. We submit that sex without at least some friction would be unsatisfying.
Aside from a lack of scientific research, there are a number of other reasons to dismiss this supposed function.
Female comfort and pleasure: If the foreskin has a unique gliding function that is inaccessible for circumcised men, then it stands to reason that studies would consistently show that sexually active women prefer an uncircumcised partner. While some surveys do show that women who have experience with both types prefer uncircumcised, other studies show the opposite. (Most online surveys suffer from self-selection bias and may have other flaws that render them scientifically unsound.)
For example, JENNIFER BOSSIO conducted a survey of 168 women in Canada as part of her PhD thesis. She reported that women "demonstrated a preference for a circumcised penis when engaging in vaginal intercourse..." and that "women with circumcised and intact partners did not differ significantly on their self-reported responses ... measuring ... pain with penetrative intercourse."  
Opponents say that circumcised men have to "jackhammer" or pound their partners in order to get any sexual satisfaction. If that were the case circumcision wouldn't have scored so well in Bossio's study. The fact is that most circumcised men don't need to be rough. They can get pleasure at different speeds of thrusting - just like uncircumcised men.
Ironically some women may find sex with an uncircumcised penis unsatisfying because the foreskin reduces the thrusting of the penis. One woman explained, "When my ex was thrusting in and out, his penis would naturally go in and out of the foreskin, which was securely planted in my vagina. Therefore you only get 1/2 the thrust sensation."  Another commenter wrote, “Many of us women folk actually prefer a good pounding.” 
Male pleasure: Studies of men circumcised as adults don't support the idea that the foreskin enhances sexual intercourse for the male partner. We caution that some of the men in the following studies may have suffered from medical issues that would affect sexual function. Furthermore studies of men circumcised as adults may not prove the effects of infant circumcision on adult sexual experiences. Nevertheless these studies seem to conflict with the notion that the foreskin enhances confort and pleasure for the male partner.
According to a study of 257 men in Zambia, 42% reported an increase in sexual satisfaction 15% reported no change, and just 22% reported a decrease in satisfaction. Almost all of the men (96%) said that they would recommend circumcision to others.  A study in the Dominican Republic included follow-up visits by 362 men between 6-24 months after the procedure. The men reported nearly unanimous satisfaction (98%), and 67% reported that sex was more enjoyable following the procedure. 
Penile sheath: Most male mammals have a penile sheath into which the entire penis retracts. However in humans the foreskin is attached to the top of the shaft and covers the glans when the penis is flaccid. During an erection the foreskin retracts to expose the glans. Sources above say that during sexual intercourse the foreskin acts as a sheath through which the shaft glides smoothly and comfortably.   [6-8]  
However there's a coverage problem. Based on an average foreskin area of 35.0 cm2 (5.42 in2)  and an average length of the erect penis (including the glans) of 13.12 cm (5.17 inches,)  certified family nurse practitioner Melanie Lindwall Schaab calculated that the the average foreskin would cover 29% of the average erect penis.  How can the foreskin act as a sheath if 71% of the sword remains uncovered?
This 2-minute YouTube video provides a demonstration of the supposed gliding function. it shows only the top two inches of the penis - the glans and perhaps one inch of the shaft - moving inside the foreskin. Even if we were to concede that a foreskin can cover 2 inches, that still leaves 61% of the erect penis uncovered.
Condom use: Most circumcision opponents downplay the medical benefits of STD protection. They say that circumcision isn't necessary because a man can just wear a condom for protection. They also insist that the most "thrilling" part of sexual intercourse is the gliding penis and the physical contact between the foreskin and the vaginal wall. Those two statements are incompatible, since the condom acts as a barrier that prevents the foreskin from contacting the vaginal wall. How can foreskin provide a gliding function when it's inside the condom? Circumcision opponents cannot have it both ways.
Writing for Doctors Opposing Circumcision Morris Sorrells explained that when an uncircumcised penis enters the vaginal canal, "the vaginal walls hold the skin of the penis relatively stable, allowing the shaft of the penis to glide in and out of its own skin sheath."  Yet when looking for data to confirm this assertion, we’re offered a study of specimens from corpses, a survey with egregious violations of standard methodology, and an "experiment" in which the researcher had sex with a Styrofoam cup.
The foreskin gliding function is a myth. The "evidence" for a unique gliding function dissolves into a mirage of Styrofoam sex and post-mortem nonsense. There is no conclusive evidence that circumcision status affects sexual function or pleasure for men or their female partners.
 Kristen O'Hara; "Sex As Nature Intended It", p 69; Turning Point Publications; December 1, 2000
 S. Ladshmanan and S. Prakash; "Human prepuce: some aspects of structure and function"; Indian Journal of Surgery, pp 134-137; 1980. (Some sources state that Parkash's name was misspelled by the printer.)
 George Hill; "Foreskin motion generates Meissner corpuscle stimulation"; BMJ; September 10, 1994. "Circumcision amputates the ridged band and tightens the penile skin, thereby destroying the gliding action that was first described by Lakshamanan and later by Warren & Bigelow."
 Jim Bigelow, Ph.D.; "The Joy of Uncircumcising! Restore Your Birthright and Maximize Your Sexual Pleasure, 2nd Edition, p 17"; Hourglass Book Publishing; 1995
 The chapter began with a quote from Genesis 1:27, 31: "So God created man in his own image, in the image of God he created him; male and female he created them.... And God saw that everything that he had made, and behold it was very good." Apparently Bigelow attempted to use a religious form of the Appeal to Nature fallacy, arguing that the foreskin must be good because God created it. Interestingly, he did not quote from Genesis 17:9-14, which mandates that every male among God's chosen people must be circumcised.
 John P. Warren and Jim Bigelow; "The case against circumcision"; British Journal of Sexual Medicine, pp 6-8; September 1994
 Gillian E. Longley; “Framing the foreskin: A content analysis of circumcision information handouts for expectant parents”, p 84; University of Colorado, Denver; 2009
 Kristen Ohara with Jeffrey O'Hara; “The effect of male circumcision on the sexual enjoyment of the female partner”; BJU International, pp 79-84; January 1999
 Andrew Gross; “Sex as the researcher intended it"; Circumcision Choice; September 7, 2016
 Steve Scott; “The Anatomy and physiology of the human prepuce”; “Male and Female Circumcision”, edited by Denniston et al, 1999
 Lexiphanic means using words that are difficult for ordinary understanding.
 D. Kim and M. Pang: "The Effect of Male Circumcision on Sexuality"; BJU International 99 (2007): 619-22
 Donald Taves; "The Intromission Function of the Foreskin"; Med Hypotheses; 2002
 Andrew Gross; "The Styrofoam Vagina"; Circumcision Choice; May 15, 2018
 .W.K.C. Morgan; “The Rape of the Phallus”; Journal of the American Medical Association; July 19, 1965. "During the act of coitus the uncircumcised phallus penetrates smoothly and without friction, the prepuce gradually retracting as the organ advances. In contrast, when the circumcised organ is introduced during coitus, friction develops between the glans and vaginal mucosa. Penetration in the circumcised man has been compared to thrusting the foot into a sock held open at the top, while, on the other hand, in the intact counterpart it has been likened to slipping the foot into a sock that has been previously rolled up."
 Jennifer A. Bossio et al; "You either have it or you don't: the impact of male circumcision status on sexual partners"; Canadian Journal of Human Sexuality; 2015
 Anecdotal evidence on social media suggests that some women prefer rough sex that involves being pounded or jackhammered by a partner. So even if it were true that circumcision eliminated a gliding action, that wouldn't necessarily be a universal hindrance.
 D.S.; comment on Pro Circumcision Parents Facebook post; August 16, 2015  C.M. comment on Pro Circumcision Parents Facebook post; July 16, 2021
 Robert Zulu et al; "Sexual Satisfaction, Performance, and Partner Response Following Voluntary Medical Male Circumcision in Zambia: The Spear and Shield Project"; Global Health:Science and Practice; 2015
 M.O. Brito; "Sexual Pleasure and Function, Coital Trauma, and Sex Behaviors After Voluntary Medical Male Circumcision Among Men in the Dominican Republic"; Journal of Sexual Medicine; April 2017
 Godfrey Kigozi, et al; "Foreskin surface area and HIV acquisition in Rakai, Uganda (size matters); AIDS; October 23, 2009
 David Veale, et al; "Am I normal? A systematic review and construction of nomograms for flaccid and erect penis length and circumference in up to 15,521 men"; BJU International; December 8, 2014
 Melanie Lindwall Schaab; "15 Square Inches?? Not So Fast."; Schaabling Shire Shoppe; June 23, 2017
 Morris Sorrells, M.D.; "The Sexual Impact of Circumcision"; Doctors Opposing Circumcision; May 2016