This is patently ridiculous.
It also explains the violence you do see. If someone believes in their heart of hearts that they are fighting for their very lives, well, then of course violence is justified. The problem is that the left is so adept at the mental gymnastics necessary to arrive at this conclusion.
Don't support taxpayer-funded healthcare? You're a Nazi. You want to see people die.
Don't support gun control? Nazi. You want to see dead children.
Don't support affirmative action? Nazi. You want to see dead and impoverished minorities.
Don't support Black Lives Matter? Nazi. You want to see black men getting gunned down by cops.
These are, of course, ridiculous notions, but they are extremely commonplace. This is why direct calls for violence from the left are accepted and even applauded.
This is why the assumption of good faith is so important, and it is also a HUGE reason why the left is losing so much support. Normal people understand that most normal people are interested in a good outcome for everyone but simply disagree on the policies that get us there.