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.
I think what we're seeing is the solidification of identity in such strong and unyielding terms that anything that threatens that identity immediately triggers a basic survival instinct. At that point, rational discourse is not possible.