The thing is, there are a bunch of different camps that support Bernie.   One way to split them is like this:  Those that are supporting Bernie because they like his positions, and those that support Bernie because they hate Hillary.  Some people are in both camps.

Trust me, most of us Bernie supporters try and mitigate the vitriol.  But I think it's important to note that a real part of this issue is that vitriol is rampant on reddit everywhere, *regardless* of the topic.   This version of it is just highlighted right now because of circumstances.