While I agree with the poster that it is good to call a spade a spade, I also think that using the word “troll” as both a noun and a verb, from a linguistic point of view, packs a whole lot of nuance into what is happening that calling someone a mere “harasser” (or most of those other specific terms) does not.
A troll is indeed, as stated by the OP, a monster that menaces whereas these are humans committing monstrous acts. But I think the thing being tossed aside in favor of clarifying speech is that many of these acts, especially when on the internet, are committed in a troll-like manner. They happen from below (where the comment section resides), they happen unseen to many (either because the perpetrator is choosing an anonymous feature or using a handle and userpic/icon that does not reflect their physical name/appearance in the real world) and they are very hard to avoid (sometimes even with help from those who should and could help).
In fantasy (which, quite a few of the old fairy tales were once intended as exercises in what my mom used to like to call the Consequences Game), a troll is what happens to young naive characters who are doing something they ought not be doing. They are not following the path. They are not going to school. They maybe are trying to do something good, but are overtaken by someone who is presenting themselves as in power and therefore entitled to a toll or fee to permit the hero to continue on their way.
This is exactly what many commenters who heap abuse (rape threats, death threats, generalized abuse) are doing. They believe they are entitled to their view and that their view is correct, so they are going to exact a toll of some kind from the person they are attacking. In many cases, they seem to feed off of the mental anguish, rather than wanting tasty goat flesh or coin.
Yes. We should call a racist a racist and a homophobe a homophobe. Should we excise the term “troll” from these self-same people (because yes, they are people) just because their skin isn’t green and warted and they don’t have exaggerated tusks as some trolls are shown? No. I think it adds a level of understanding to how horrible they are.
(As an aside, some of the early drawings of trolls in fairy-tale collections I remember the clearest are the ones that looked the most like angry white men wearing a loin cloth. They were black and white sketches; until the text told me they were green, I didn’t know they weren’t men.)