A Good thoughtful post Joe.

"It's my impression that there is an underlying threat of violence in all that the alt-right says and does. I would like to think that is not the case with the Left, but I think we have to admit that sometimes we have failed, and some of those on our fringe have used demonstrations as an opportunity for violence.

Not just on the fringe I'm afraid.....this forum contains well educated intelligent people mainly of a pretty advanced age.
One would expect circumspect comment here, but there has been expressions of hope for the death of the President, several supporters of terrorism to achieve political change, abuse of anyone who dares to reason against violence by branding them as traitors to the "liberal" cause.   Even Don exhorting us to be brave and go into battle.

You live in a deeply divided country, and it was so long before this presidency, the two wings of the government bird tried to obscure the truth, in fact they used it unashamedly to divide the people and gain political advantage.
If the debate is brought out into the open there is a chance of the unity which is required to avoid violence and civil unrest

Our political parties play the same game but it is becoming redundant, we do not have your history the hatred is not so bitter....we have to all intents and purposes become politically and socially colour blind. Our arguments over immigration have nothing to do with race, only numbers and regulation.

With a little understanding of alternative views the same can happen in the US.