Could be, but given how intensely angry they get about it, I have to think that there's more going on. At a guess, I think part of it is that Man Box (or toxic masculinity, if you prefer) dictates that men don't complain, and that men have to be hyper-competent, especially when it comes to sex, and they can't entertain the notion that anything about an intact penis could be better in any way.

I figure some of them just don't want to admit that they're missing a part of their "manhood." Maybe there's hidden resentment, maybe they don't want to admit their parents made a mistake, but at the end of the day they're hearing that others' penises are "more intact" than theirs, and that might be tough to accept.

I'm speculating to an extent - I don't have a penis, but it's not difficult to imagine the complicated feelings some circumcised men go through upon learning of what they've lost had taken from them, and that there's nothing they can do about it.

I wouldn't be surprised if the same thing happens to some women who've experienced FGM. They went through a horrific practice and can't come to terms that they might "have less" than others, so they double-down on the idea that what they went through must be okay.