I think it is due to the severe anger, hatred, vitriol, and lack of ability to see other viewpoints that seemingly more on the left possess than the right. Certainly both sides have groups than are way extreme and hateful, but there is no doubt the intolerance level is escalated on the left.
Agree to Disagree...from my personal experience, I have encountered the opposite. I have said many times that I am an independent, but lean Left (most of you probably see me as Liberal cuz of my views on Trump)...My conservative friends; in which I have many act like I'm a Lunatic Liberal (ha). I have on occasions gotten into conversations with friends of friends, and when my Republican friends tell them I'm a "Liberal" the name calling starts (snowflake, socialist, Lib, crybaby, freeloader, etc) and the generalized attacks (oh u want everything given to you, you don't want your freedom, no guns, etc.) I promise you this has happened more than a couple of times...I tell them I don't agree with either side strongly, but that doesn't matter, cuz I'm not Conservative. So I know there are crazies on both sides, but I feel Conservatives truly can't understand how others don't agree with them (again, these are personal experiences)