Why is Keith Olbermann so angry all the time?

There are bad talking heads, then there is olbermann. this freak is in a league of his own and he makes me miss seeing rosie o'donnell on the view. Every single night he makes a 15 minute "special commentary" about some person or issue. It's a very long and thought out hate rant against someone...Hillary, Bush, McCain...anyone but Obama of course. He seriously scares me. He was screaming for Bush to shut the hell up the other day and he was spitting at the tv camera and I was hoping he was going to have a stroke so he would shut the hell up himself. Aren't liberals embarred to be represented by people like this?