Published September 12, 2020
Revised October 4, 2021 Intactivists say that a circumcised man doesn't know what he's missing. 
That's true - to some extent. A happily circumcised man doesn't know that he's missing phimosis and smegma. He doesn't know that circumcision reduced his risk of urinary tract infection during infancy by 90%. He doesn't realize that circumcision during infancy lowered his risk of penile cancer by 99%.
He isn't aware that he spends less time cleaning his genitals. He doesn't know that his penis lacks an unpleasant odor. He's less likely to know the shame of being asked to wash his penis to remove the unpleasant odor prior to sexual activity. He'll never know a partner who refuses to perform oral sex on account of his circumcision status. He won't know that circumcision reduces his partner's risk of HPV and cervical cancer.
A happily circumcised man will never know regret for his parents' decision. He'll never have to pay $2,000-4,000 for an adult circumcision. He'll never know the embarassment before, during, and after the procedure. He'll never have to take time off from school or work for the operation. He'll never know how much pain he would have suffered during and after the procedure. He'll never have to abstain from sex for several weeks during a recovery period.
What's really going on here? The overwhelming majority of circumcised men are happy or unconcerned about their genital status. Most circumcised men insist that they are fine. Unfortunately for the intactivist movement, these men are of no use to them.  The conundrum for intactivists is what to do with these millions of happily circumcised men.
Circumcision opponents deal with this problem by trying to discredit these men. They may accuse a circumcised men of being ignorant or culturally biased. These are just ad hominem attacks intended to discredit the testimonies of millions of happily circumcised men.
Another method intactivists use to discredit circumcised men is to claim that these men are in denial about the harm. Rather than consider the possibility that they themselves are mistaken, intactivists reflexively accuse happily circumcised men of denying that they have been harmed. Intactivists will claim that - deep down, every circumcised man knows that his penis is inferior to an uncircumcised penis; but his fragile male ego prevents him from admitting that truth. Instead, he denies the reality of his sexual predicament in order to protect his ego. Denial is a psychological coping mechanism that involves avoiding a confrontation with a problem or reality by denying the existence of the problem or reality. This self-serving accusation is dependent on the premises that circumcision is harmful and a circumcised penis is deficient - which are the very issues in question. It's a closed circle argument, "one where there is no possibility of convincing [intactivists] that they might be wrong. They are right because they’re right."  A closed circle argument, one that is unproven and unfalsifiable, is meaningless.
The statement that happily circumcised men don't know what they're missing is a logical fallacy called begging the question or circular reasoning. It is based on the disproven assumption that circumcision reduces sexual performance and pleasure. Several articles on this website address those claims. [4-9]
Experiences of uncircumcised men
The experiences of uncircumcised men can provide additional evidence that circumcised men are not missing out on pleasure. One man explained, "Having a foreskin has not made me feel any more 'complete' as a man, and in fact is actually frequently a nuisance. To all men who are circumcised: you are not disfigured. You are not incomplete. You are not inadequate."
While there is no direct association between men circumcised infancy and those circumcised during adulthood, the latter are uniquely qualified to compare their own sexual experiences with foreskin and without foreskin. Their reports suggest that there is no automatic correlation betwen circumcision and sexual harm.
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.  Researchers surveyed 2,784 men in Kenya at various intervals following elective circumcision. After 24 months, 64% reported that their penis was “much more sensitive", while just 7% reported that their penis was much less or somewhat less sensitive.  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. 
Circumcision opponents cannot have it both ways. If we must listen to and validate the complaints of a small minority of dissatisfied circumcised men, then intactivists must listen to and accept as valid all statements by the overwhelming majority of satisfied circumcised men.
 See for example: Ronald Goldman; "Why Most Circumcised Men Seem Satisfied"; Circumcision Resource Center. "Circumcised men do not know what they are missing. They believe that the sexual sensitivity they have without a foreskin is 'normal.' (Similarly, a woman born in Somalia who had been subjected to a severe form of [FGM] insisted that it had no impact...) According to one man who was circumcised as an adult, sex without a foreskin is like sight without color. Those who have not seen in color cannot appreciate what is lost."
 Colton Harrelson; Intactivist Trauma Relief Facebook group post; February 4, 2019. "It is unacceptable that there are people who are circumcised and happy that they are circumcised, and appreciate it. It is important that every circumcised man feels like we do so that progress can be made into banning routine neonatal male circumcision." See also: "Is there an intactivist tipping point?"; Circumcision Choice; November 2, 2019.
 David Didau; "The closed circle: Why being wrong is so useful"; Learning Spy; October 30, 2015
 "The 16 Foreskin Functions - a critical analysis"; Circumcision Choice; November 22, 2017
 Andrew Gross; "Of all the nerves"; Circumcision Choice; March 3, 2018
 Andrew Gross; "The Styrofoam Vagina"; Circumcision Choice; May 15, 2018
 "15 square inches of erogenous tissue?"; Circumcision Choice; March 21, 2020
 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
 John N. Krieger M.D. et al; "Adult Male Circumcision: Effects on Sexual Function and Sexual Satisfaction in Kisumu, Kenya"; Journal of Sexual Medicine; November 2008
 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