Trolling Bloggers

What is it about troll bloggers? What sort of person trolls through blog sites looking for people to heap abuse on? I know it's easier to tear something down than it is to build something, but why devote an entire blog to the kind of harsh criticism that causes a long-term blogger and down-right decent guy like Christian from Destination Unknown to close down his blog?
I work with people like this all the time and like to think I have a fairly good handle on them psych profile wise. To me, it's an indicator of social isolation, feelings of helplessness and lack of control in the trollers own life and potentially the concept of "lack of voice". I like -and appreciate- some honest criticism, but this sort of vitriol is just pointless, disgusting and nihilistic. Sure, you could argue that any publicity is good publicity, but to quote Yeates, "Tread softly, because you tread on my dreams".
Bye Christian. I'll miss you dude.