I think people should behave on Facebook more as if they were at a dinner party. Facebook is a social medium where there are no normal social consquences, unlike that dinner party. You can say anything you want, and you aren't not asked to the next dinner party as a result - you just keep posting. You just get to keep talking. Unlike normal life, where if you insist on inflicting your political views on people, they stop inviting you over for a meal.
It's useless as a platform for putting political beliefs out there - we just skip over the political screeds. Because it's not dialogue, it's just a megaphone. Dialogue is conversation, and Facebook ain't that. And when was the last time you welcomed someone with a megaphone to your dinner table?