cutting isn't a mental disorder. it is a symptom that occurs in a mental disorder, to be sure, but there are symptoms that occur in mental disorders that aren't (when they occur in isolation of other symtptoms) regarded as problematic at all (hypomania, for example).

lots of cultures have 'rites of passage' into adulthood. adolescense (a protracted period between childhood and adulthood) is a very recent invention indeed. in other societies people might go on their first hunt at 11 or 12 or whatever - and if they participate effectively then they are regarded as a man from that point. baring ones 'battle wounds' to eligible (or soon to be eligable) girls / women (and getting their sympathy / awe / respect) would have been an important thing to do.

rites of passage into adulthood are typically rather gory... my supervisor was talking about this tribe the other day (trigger warning) where the boys were circumscised with a stone when they were 13 (or however old). their living through that was their passage into adulthood. after that happened... when the wounds were healing... it was a ritual of the culture that the girls would sneak into the boys room and try to stimulate them to erection (thus bursting their new scars). the 'manly men' were the ones with the most scars.

the 'favour' is returned with marriage, however, where the cultural ritual is for the guy to have brutal sex with his virgin wife (as brutal as possible). the more blood that was found the next day... the more 'manly' he was (and of course the more 'chaste' his wife had been).

An interesting take on the origins of violence (and an interesting take on the EQUALITY BETWEEN THE SEXES that was impliclit in the reciprocal brutalisation). My supervisor thinks that those kinds of rituals act as 'fitness traps', basically, where there is an initial advantage to individuals who adopt the custom (feet binding / female circumscision were costly signals of quality when only adopted by a few) but when everybody adopts them for their fitness value the whole culture bears the cost and no individual benefits significantly since everyone is doing it.

I'd imagine that in adolescents resilience to pain is something that is looked upon with awe / admiration. Our long evolutionary history... WOuld predict that that would be so. In some cultures (warrior cultures, for example) a person would be signilling their high quality / the liklihood that they would achieve high status later.

Our culture runs a little differently now (well, some aspects of it do at any rate). But old habits die hard...