I tend to keep a low profile out there in the wilds of Facebook. That doesn't mean I won't correct or challenge someone on something, but I don't press on any further than that. And I leave differences of opinion completely alone. Or mostly alone. I think. I think I do. I mean, more or less.
BK's example, and Laura's example, and a multitude of others, show how dangerous it is to say just about anything among people you don't know and who don't know you, or any other situation in which a basic understanding can't be easily attained.