There's stupid, there's weapons-grade stupid, and then there's the Facebook Political Argument. If you've never been in one of these, consider yourself fortunate for having avoided the online equivalent of slamming your head into a tree. If you have been in one of these, let me enlighten you:
You think you sound like: Pithy statement, followed by carefully reasoned argument, added to a dose of genuine wit. Everyone reads, and "likes" your quote, because you have enlightened the Facebooksphere.
You actually sound like: Nasty trollish comment, followed by straw man argument, added to a dose of ad hominem attack, sprinkled with pure douchebaggery. Some bored idiot reads, and "likes" your quote, because they're sure it'll piss off the conservative/liberal who has to douse their eyes with bleach to unsee the awful and stupid thing you just wrote.
Both the beauty and the curse of the Internet is its unregulated nature, meaning all statements have equal footing, whether you believe that a change in the tax structure could benefit key parts of our economy or you think the Devil is literally on the rise in the opposition party. It's like cable news, except broadened for everyone with an online account.
It's easy to say that next time you see a political argument brewing on Facebook you should just ignore the bait and let the cranks go back and forth. But what do you do when your otherwise benign post gets threadjacked by commenters into a political bog? (Say you make the original post "Happy Memorial Day Everyone" or "Avoid Chicago's pizza because it's crap" and your friends comment "Memorial Day only serves to support our needless wars!" or "Chicago makes pizza as bad as they make presidents! NO-bama!") Here are some options:
1) Delete the comments off the thread. This is a pretty cowardly way out, though. Anyone noticing that the comment was deleted is going to think you're a hypersensitive wuss who shrivels in fear at the sight of glorious dissent! Even if the dissent itself is completely stupid.
2) Respond to the comments as they are. Point out that "no, Phil, Memorial Day is more about supporting our war dead regardless of the cause because they sacrificed for our country, and frankly as a big FDR supporter I'd think you'd be okay with targeting civilians in our bombing raids, after all he seemed just fine with that you hypocritical idiot" or "if Obama was really as bad a president as Chicago's 'pizza' tastes, then he would have accidentally nuked California by now and stapled his own foot to the Oval Office floor".
3) Get the comment thread back to your original point. Say "I'm just acknowledging that on a day I can eat hot dogs and drink beer in my yard with friends it'd be nice to take a moment to think of those who cannot do that because of what they sacrificed to this country" or "what the hell does Obama have to do with gross gooey pizza pot pie?"
4) Ignore the comments and just let other commenters swirl everything down the drain. This is generally the best approach. It allows the dumb comment to linger on for all to see, and speaks only for the commenter. Because frankly, there's nothing you could possibly write that would make such a commenter think "hey, good point. You've given me much to think about."