The abject denial of left-wing violence in the media and the correlating hysteria about right wing violence is disturbing and is obviously fueling the false sense of self-righteousness that is driving that very violence. Anyone with a shred of integrity denounces ALL violence, even if the perpetrators share your ideology.
To help burst anyone's delusions, here's just a few recent left-wing violent incidents off the top of my head.
http://www.eastbaytimes.com/2017/05/24/berkeley-college-prof...
https://www.nytimes.com/2016/07/10/us/dallas-quiet-after-pol...
http://www.cnn.com/2016/07/17/us/baton-route-police-shooting...
https://www.rt.com/usa/366452-portland-riots-anti-trump/
https://www.wsj.com/articles/the-mob-at-middlebury-148858650...