I'm assuming my reasons for being their friend were not "Oh, they aren't a racists!" or "Hey, they support gay marriage, so obviously we're friends."

If you only had friends that agreed with you on every topic, you wouldn't have any friends.

Yes. I do have friends exactly like that. I'd only cut them off if I decided to fight for a cause, and they were getting in the way.

I have lots of friends I troll..., I mean...., whose views are different than mine.

All that is necessary for friendship is for two people to find some sort of concordance. It could be as small as having one thing in common (like they attended the same summer camp) or it could be a whole lot more. It's up to you whether you cut people out for not being just like you, but I wouldn't advise it.

I recently just lost a friend over an argument that, in my opinion, was more a debate then a full blown argument. I think having friends with different opinions makes life interesting, it'd be boring if everyone agreed with the same thing and it helps a person to grow or see another side of things. What really matters is the maturity of the person you have clashing opinions with. If you can each respect each other for the differences then there shouldn't be any issue.