Like Taylor said, I think it depends on where you go, but I can speak from my own experience.
Like many colleges, the one I will soon be graduating from is left-wing. Although most of my professors aren't blatantly liberal, it's not hard to tell what their political views are. I've had a few professors that were more open about it though. I had one macro economics professor who would rant and curse about how the younger George Bush stole his retirement money. He opened class by showing us a clip from the Daily Show, and some of the questions on his tests amounted to us explaining to him in detail how Republicans ruin the economy. Quite an amusing class, and a great way to earn a math credit.
As far as the overall atmosphere of the college goes, we're extremely welcoming of minorities and everyone on the left side of the political spectrum, but when it comes to anything on the right... eh, not so much. You won't be blatantly discriminated against, but your opinions would pretty much get dismissed out of hand in a lot of contexts. I know a lot of people who openly mock and belittle anything and anyone right-of-center. I'm a liberal, so it doesn't bother me much, but I could see it getting frustrating for anyone who held those views.