I think they do it because feminism threatens their perceived "rights" as men, or roles as women.
It's quite interesting observing some of these people. They open accounts daily, and ask inane questions. One example - "is it OK that I kicked my boyfriend in his testicles". What they hope to achieve by this, is to make women look ridiculous, so that they can justify their hatred of strong women. Unfortunately for them though, what tends to happen is that the women they so desperately want to demonise actually answer things like "No, it isn't ok to kick his testacles" They get frustrated, and do it all again under a different account several days later.
I used that example, because what strikes me about this little "strategy" is that they have such little "ammunition" against feminists, that they have to *create* scenarios for their little self fulfilling prophesies. You'll see it again and again in the many accounts they create with female avatars asking and given inane responses.
So, why do they do this? Because they are scared, and probably because they're a little immature, (which is evidenced in their questions such as "if women can go to a women-only gym, why can't men?")
One thing to remember though, they represent a very small percentage of society (the trolls, that is) and most *normal* men actually like women.