Are you suggesting that there are populated places that you can visit in real life where loudly shouting an arbitrary statement could not attract abuse?

If I went to a model train convention, carrying a giant sign explaining how childish and stupid I think model train enthusiasts are, do you think I would be subjected to a "constant barrage of callousness" until I left?

In the UK, "trolling" has been entirely defined (by a media and political class full of blue checks) as any angry response of the public against the wise observations of blue checks. It's entirely class-based. You don't have to threaten, you don't have to swear, you don't have to be ethnically, religiously, or sexually bigoted. You just have to strongly disagree. In fact, the more biting and incisive the comment, the bigger the perceived offense.

Entirely about nobodies embarrassing somebodies in public.

edit: this is a special meaning within the UK media and political classes. Generally, "trolls" are people who like to cause arguments online, and who can be judged by the ratio of the number of characters they type to the number of characters they cause to be typed. "Trolls" are not people who have an honest belief in what they are saying. It's only in the UK (AFAIK) where "troll" is defined by disagreement and exacerbated by tone.