Oh, honey, do I feel your pain! All these old high school "friends" found me on FB and, well, I'll put it this way: I now remember why I moved a thousand miles away!
First I ignored it, then I challenged a couple of the people who really posted crazy, ignorant, intolerant sh** up there. Finally, I hid them from my newsfeed. Life is too short. I won't change their minds, and it just upsets me. I feel like it's rude to confront them -- since it's their page, and they can say what they want -- but some of the stuff they post is so awful that I feel like I HAVE to challenge it if I see it. So I'm happier if I don't see it.
If I actually knew them better, I might try to engage in dialogue with them..... but they were borderline friends as is.
(I have to admit, though -- every now and then I "unhide" them, just to see what's up there. It's like a painful scab I can't stop picking at....)