Fringe extremists on the right are deemed to be a major social crisis requiring all hands on deck to oppose, both by being very "vocal" about it, but even through violence,  while the extremists on the left these very same "alt-right" extremists are reacting against, are not...?

But while the extremists keep upping the provocation to the other side,  the moderate middle is expected to pick a side and join in the din. 

Sorry, I think we should quietly shrug off both extremes, but say, "a pox on both your houses".

And I don't share you pessimism about rational debate. While many on both sides have already made up their minds, rationally or not, I think many people are quietly listening to the debates, trying to decide who makes sense and who doesn't. It matters which way they get convinced, but insulting them isn't going to win anyone over.