I agree that there are people on the left who are mean online and that they shouldn't generally act this way. I just think that
1. This largely ends here (there are exceptions, and it is definitely no fun to be yelled at online)
2. The right has consistently acted in all of the same ways (plus more bomb threats) to no similar criticism
3. The political strategy of the left cannot require "literally everybody online is on their best behavior all of the time."
And no, law enforcement is absolutely uninterested in dealing with death threats sent by people who think that doing research on climate change is evil. The idea that the FBI would help out is odd to me.