It is important to realize that even as we disagreed, we still used to agree on basic facts and then fought over what best to do next.
That is what is different now! We now live in a culture where any discussion can simply be ended with "Your facts are wrong", or "I have alternative facts". A reasonable discourse is not possible this way.
It takes just one "side" to take such a stance for society to fall into camps. I think that is what we see happening.