[If we are working from the premise, that gender is theater, then the question is: theater in service of what?]
So initially, the purpose of masculinity, may have been to protect against nature. But I imagine that was a small role (nature was pretty abundant -- the threat of wolves and bears and snakes and things has always been smaller than the threat from other people). Mostly the purpose of masculinity, and the reason it is still valued, is because it offers protection. But protection from what -- other people displaying masculinity.
That seems pretty ironic.