If everyone is born feminist, where did this allegedly sexist society come from in the first place?
You are neglecting to account for the entire field of biology and genetics, as well as making feminism sound like some sort of creepy religious cult (although it's certainly starting to resemble that, recently). People aren't really a blank slate at birth. Nature and nurture are fundamentally intertwined.
Additionally, what a "feminist" is seems to vary widely, from "thinks people should be equal" to "we should exterminate men." Your claim seems ludicrous in light of the fact that even feminists do not seem to know what exactly a feminist is.
Recently? :) Find some articles and pictures from the '70s.