I remember reading a thread somewhere (here, reddit, somewhere on the internet) about a woman who discovered her husband would go online and troll. Not innocent, innocuous trolling, but finding videos of young girls on youtube and calling them names, being directly verbally abusive, etc.
His wife thought this was insane and completely out of character for him, she couldn't believe it until she read what he was writing and verified that it was him. She confronted him and learned that it was his self-professed outlet for stress. She asked him to stop, and it wouldn't, and it led to their divorce. All because this guy was determined on being a total fucking cunt on the internet to other people.
I don't really know why people do things like this, or how (if) we can prevent it, or what actions we can take to mitigate it. It's a problem, though. People need to treat eachother with respect and empathy, even if we disagree. I believe Anita's actions are a net positive force on humanity, especially in our little microcosm of society. I hope that she will continue bringing her discussion to the table and that others will follow in her footsteps, despite these scumbags who exploit their anonymity to create fear and breed hatred and misogyny.
edit:
Here's the post about the wife and husband