Also, I believe that we're constantly hearing so many voices trying to convince us one way or another, that our own discussions on those topics end up being attempts to convince others. That would explain "safe spaces" to some degree -- people don't want the pressure of having someone else try to convince them of something they don't agree with.
Some of it just the two-party system. The points don't matter, just which side of the line each person is on. I wonder if more parties would help depolarize the situation. I'm really not sure.
The problem is, if we're talking in a public forum, anyone can come up (from side X, side Y, or both) and jump in not in good faith. And so I get, as Fellshard said, my hand chewed off, not by the person I was talking to, but by a bunch of drive-by conversation-killers.
Under current conditions, I don't think a real conversation can happen in public (which includes social media).