No one would ever consent to doing it once they're old enough to feel and remembering, no matter how beneficial. Thus, pre-memory is the only time it can really be done.
Doesn't that imply that it's not something that should be done? I mean, if no one (and that's a bit of an exaggeration: adult circumcision has existed in several places) would be willing to do it if consent is an issue, doesn't that imply that they find having their genitals mutilated an inherently problematic practice?
Well, if this were a new procedure, I'd agree with you, but it has been a well-established procedure for literally thousands of years and has been shown (arguably, I know) to have benefits. Also, I never see men who were circumsized as infants complaining about it as adults. It's just a no-big-deal kind of issue.
Also, calling infant male circumcision "mutilation" seems to make light of the real horrors of female genital mutilation in other countries. Not even close to comparable there.