So glad you decided to share this, as hard as it must have been. Thank you for being so positive.
Just yesterday I was talking to hubby about why people feel the need to post a nasty comment on something they don't like when most would just go past it or block it if they disagree with it. He told me that his friend (and this was unexpected as he's always polite to me) does things like that because he likes to get a rise out of people. He sometimes does it to hubby, but when hubby tells him not to be a c**t he apologises. He's not physically strong, in fact he was likely a target of bullies himself at one point. He doesn't always keep his insults to himself in the real world either and ends up getting smacked occasionally! Alcohol probably doesn't help his decision making.

Anyway, I mention it because, as you said, it isn't about you, it's about them and some people are completely oblivious to the effects of what they're doing. They are just trying to find some way of feeling important themselves.