There are such things, and they are frightening. Someone mentioned here a while back the case of Justine Sacco, who said something stupid on Twitter, and was ruined for it. You can read the whole story in this New York Times piece, which also includes stories of other people who made the wrong sort of joke in the presence of the wrong sort of person and paid for it with their jobs. Possibly the most striking thing in the piece, though, is that the author is a former participant in such mob actions, and thought them entirely justified when aimed at "powerful institutions and public figures." And it wasn't clear to me whether or not he still sees it that way.
I have to admit that I was slightly shocked that people deliberately stir up these things. I had supposed they were more spontaneous than that. Most disturbing, there are in fact groups who monitor the internet activities of their ideological enemies and attack them at every opportunity. Here is the account of one victim, Robert Oscar Lopez, a bisexual man who "had nothing against gay relationships, but didn’t think same-sex parenting was fair to children."
The idea that bringing people closer together is a step toward peace always was a bit naive.