You could argue that 4chan (as instigators in Adria Richards' harassment) aren't "normal people in a normal online community", maybe slightly less plausibly wit

You could argue that 4chan (as instigators in Adria Richards' harassment) aren't "normal people in a normal online community", maybe slightly less plausibly with Twitter users. But I see embryonic mobbing instigations on my Facebook all the time. I see middle-aged mothers posting horrific violent imprecations and "find out where that person lives" in response to news articles about some outrage or another. Ordinary people have this hate and desire in their hearts and aren't embarrassed to show it.