At this point, I generally assume that those who go after others for small things online for seemingly no reason are:

1. Bot accounts. You know, the ones where one person controls 20 accounts and uses them to dogpile others?

2. Empty and unhappy people.

3. Find some kind of fulfillment from even negative engagement with others.

4. Are just jerks.

Either way you slice it, I feel bad for these people. I certainly have my flaws but I really do my best to be decent to others, especially online where it's much easier to be impolite because you're not face-to-face.