Are you sure about that? When I sign on to Facebook, it appears to be social media for middle-aged liberal minded people. Facebook is a bit of a mirror in that sense.
Exactly. Almost the only time I see things that I disagree strongly with is when I'm shown a comment by one of my contacts who is in a stupid fruitless argument where neither party has a chance in hell of changing the other persons mind.
It has become pretty good at only showing you things you like to counter the reputation of making you hate the people you know IRL, I suspect.