Even with Internet Anonymity Theory being a factor, Jerry doesn't curtail his audience as well as he thinks he does given how often he proposes violence and advocates death and fatal beatings towards people his doesn't like, both on his YouTube channel and his Tumblr. It's no surprise that being an advocate for violence publically influences your audience to have violent tendencies.
I'm actually really glad you brought this back up, because I was just musing about this very point earlier.
He has no one else to blame but himself for his fans' shitty behavior. I mean, what else are they supposed to think? Especially when you say shit like:
"All Nazi's should die!"
"Josh is a Nazi!"
"Josh reblogged a post joking about Trump on election night! #DIE" (Actual post, actual hashtag)
"Josh is a whiny Trump-supporting coward with a neoreactionary fanbase who deserves all of the criticism and beatings he can get."
*An impressionable fan listens to this*
*Said impressionable fan, with a false idea of who Josh is, decides to commission a piece from Lizzy with them slitting Josh's throat*
"This is fucking disgusting. You all need to be kept in control."
But he's obviously too narcissistic to believe that the slanderous shit coming out of his own mouth is why his fans will go and "attack" (see: say mean things to) other people, and why people will have the desire to commission some kind of sick murder-fantasy about someone they've been conditioned to believe is a reprehensible human being. And he calls Josh's fanbase "rabid".
TL;DR it's Jerry's fault people in his own audience apparently have violent fantasies about killing Josh.
inb4 he calls this point "reductionist"