First, cultures adapt much faster than ecosystems. You wouldn't object to an ecosystem adapting. So where do you draw the line between unwarranted homogenization and cultural evolution? Dealing with similar conditions, we'll develop in similar ways. (And our conditions globally are getting more similar; the main impositions are economic, not military or political.) And so it is with female genital mutilation here and there, conditions change, understandings develop, resistance grows, abolition ensues, backlash follows, and so forth. Internal to that culture, the arguments will be made about survivability, just as we have the argument here around gay marriage, the end of the family and all that. You can't put a culture behind glass like a butterfly on a pin.
Second, humans did evolved with the human female having sexual desire and the capacity for sexual pleasure. An argument could be made that that capacity might've _helped_ keep us going when we were in danger of getting wiped out--gotta be some payoff for sex when the prospect of childbirth is difficult (at a point where sex and childbirth were known to be related). Not to mention sociability and social cohesion. So there's something there, too.
Jenny Brown