Let's see. Could it be because he's a "socialist?" Well, some of them don't have a clue what a socialist is, and probably are dumb enough to believe the hype from Fox; but would a socialist get all that Wall Street backing?
Oh, wait! It must be because he's an abortion slinging, gay loving, social radical! Mmm... maybe not. He never talks about the "choice" vs. "right to life" controversy, still hasn't publicly endorsed gay marriage, and took a hell of a long time to end "Don't ask, don't tell.". Granted, he's not religious. He doesn't do all those church appearances we've come to expect from our presidents, and the connection to Reverend Wright was nothing but Chicago political expedience. Okay, it's clear he's not a social conservative. Maybe that explains some of the animosity.
Well, then there's the little matter of the blackness. That's reason enough for most of the white south and entirely too many working class white men, but it still seems inadequate to explain the extent and the intensity of the hatred. It certainly is not enough to ensure a Republican victory.
As you may have noticed, I haven't been too enthusiastic about him myself, for none of the above reasons. On the other hand, he's a mile above any of those assholes trying to win the Republican nomination (albeit John Huntsman wants to break up the big banks, and that goes a long way with me. I haven't heard it yet from Our Esteemed President, sure as shit.)
Actually, I suspect they hate him because they're taught to hate him — by Fox, ALEC, the Koch brothers, et al. I have to admit, that cabal does a pretty good job of it. Still, even with all the money in the world (which they seem to have,) it's hard to get someone to spring such a a really stiff hate-on unless there's some initial antipathy from which to work.
And, as you may have noticed, he kind of looks black.