Without any rhyme or reason for it.
You are spending too much time and effort attempting to characterize why people decide to troll. Sometimes people just enjoy poking fun at the self righteous know it alls that like to post their thoughts on comment threads.
I find exploring the causes of human behavior very fascinating, but more than that light needs to be shed on the causes of destructive tendencies. Abuse, neglect, absent fathers are having a more catastrophic effect on American society than we even realize. Internet trolling is just one symptom of a greater disease.
Unless you thought crazy animal rights activists, PETA members, Antifa thugs, drug addicts, etc. just sprang up out of nowhere...
I doubt it. More likely it is a new behavioral pattern that results from indirect, long distance interaction between people in one of the many new contexts created by the internet.
You may feel that modern society is "diseased" in some way, and that may be a reasonable characterization of some of its aspects, but I am not aware of any data showing that internet trolling is anything but a new behavior pattern.
If it is a "symptom" then what is the disease?
“...on the causes of destructive tendencies...”
Sometimes, there ARE no causes, friend. Some people are just ... twisted ... and get their jollies being d*ckheads. It’s a power trip, I guess.
You are correct, though, about some causes. But... Human nature is a bizarre thing, and there are simply times when there IS no explanation for why people do what they do.