Feminism, in general, is biased against men in the same sense
that giving a short person a box to stand on at a concert so he can see the stage, and not giving a box to a tall person who can see just fine already, shows bias against tall people.
This is just like a lot of feminism. Feminists arbitrarily decided that men's lives were better than women's, and wanted to make it possible for women to lead men's lives. Personally, I consider that being at home is better than being at work, but feminists hardly ever fought for the ability of men to be stay-at-home dads.
It's positive discrimination (which, coincidentally, is how affirmative action is described) but discrimination nonetheless.
I'm not judging. I just thought I would share because I find it useful to remember.
The thing that keeps them from participating is men bullying them and forcing them out.
In reality the real goal should be making the short person grow to be equal height.