It’s not only online. Just last weekend, someone heckled me at Costco because my wife was pushing a heavy ass cart while I was walking freely next to her. She chose to do it, I offered to take it and she refused. But somehow a random stranger had something to say about it.
Online behavior is unfortunately a slightly worse mirror of real life. If you want to experience people outside of your bubble, just go to any public hearings or meetings and you’ll find that a lot of people are quite out there.