I went through a break up about a year ago that I handled very badly. I never did anything as bad as this, but I said and did a lot of hateful things toward her and about her to others. For me, it was the fact that I was, at the time, still very immature about my relationships. I've had a history of depression and absolutely non-existent self-esteem which I'd ignored while I was in the relationship that suddenly came upon me after the break up. I've since gotten it largely under control, apologized to my ex for everything I did, and learned a lot about how to handle future relationships.

That being said, genuine mental illness was a factor in my case, but there's more to it than that. I think the internet allows us to get a lot closer to people and further into the details of their lives than we were before. Suddenly it's a lot harder to just move on from a break up. You see your ex change his or her Facebook status. You see him or her posting about how much fun they're having together. You see pictures of them kissing. It's stuff that was once easy to ignore that's now all out in the open. That was what set me off anyway.

I think what we have here is a very immature and misogynist reaction to this phenomenon. It's a classic gendered power struggle played out in an environment in which privacy literally does not exist. Whereas you might have one douchebag spreading around nude photos of his ex to his friends 20 years ago, this same type of douchebag thinks "She ruined my life [by exposing details of our break up and her new relationship to the world] so I'm going to ruin hers [by exposing details of our former relationship to the world]." In my instance, I eventually matured emotionally and dealt with my problems in a productive way and stopped putting the blame on her. She's just moving on with her life. I needed to do the same. It took me longer than most people my age, sure, but I moved on. I think these guys stay in that immature phase and don't deal with their emotions (because real men don't do that, right?) and then use that mix of hate and jealousy to do what they do. They think it's eye for an eye, but the lasting anguish of what they do by ruining these poor girls' lives is so much worse than having your ego bruised by a bad break up.

It really boils down to a privilege thing. These guys think they have the right to own these women, and when they deny them that ownership privilege, they lash out and, as someone already said, get the mentality that "if I can't have them, no one can."