You misunderstand. I think there probably is some bias against women going into mathematics. When someone say "let us take this as true for the purpose of argument", it does not mean that it isn't really true. It means simply that in this post, we're not going to analyze the possibility of whether that is true or not, we're just going to assume it.

There's also a class of people who are so smart they see sexism uniformly everywhere, even where it isn't. You're being a jerk, not proving how wonderfully not sexist you are. Refusing to even consider the possibility that someone isn't sexist is itself a form of discrimination, and I reject your attempt to pigeonhole me in an effort to make yourself look holier-than-thou.

I'm also not going to fall into the trap of endlessly justifying myself, so go ahead, have the last word.