It’s a battle. There are antibodies and there are advocates.
Here’s a depressing story about it: https://www.usenix.org/blog/my-daughters-high-school-programming-teacher
One lazy person who doesn’t meet the challenge can harm everyone.
And here is an awesome story:
http://www.nytimes.com/2013/09/08/education/harvard-case-study-gender-equity.html?src=me&ref=general
Tackle all the whiners and opponents of change. It can be done.
But you have to fight all the battles — including the locker room and the bar and the other clubs.