IMO, there's a lot of factor playing part in this. (Copying from my fedi personal fedi acc!)

1. A lot of people lack control of the real world situation that happen to them and some are desperate for the feel of being in control enough to harm other people just to feel like 'I'm in control'

2. A lot of people do not have a way to properly deal with their anger and frustration. They only teach to 'hold or suppress it' and there's such also consequence in showing negative emotion IRL, so online is almost having no consequence for it.

3. Online people are separate by screen. People know that there's people behind it, but they don't feel it. In online, we don't get in your face 'feedback' from body language or facial expression from other people. IRL, you mess around and pretty much find out instantly.

4. Social media reward people with engagement and fav/like, which is easy dopamine for people like it's just a tip away from their body. And SOMEHOW I feel like social media normalized people being mean to each other as 'Playful witty funny hahaha' so they get rewarded by that. And yeah these things are addictive, so you can crave more, making you do more 'extreme' thing to get them. And yes you can get addicted to being angry too.

5. And then there is also peer pressure and 'us vs them' mentality that is so strong in social media. I mean yeah, if we look at it, being 'mean' together with your group it's sort of activity that you can bound together and also reward you as well. It just not a good one and come at a cost of another people.

Now add all of them together, you get the platform that reward toxic interaction and also extremely addictive. You get reward from like/fav. You get reward by 'Peer approval' (because today we forbid other people having neutral opinion on a thing, but it could be just my experience.), You get reward by your own brain. Not counting other thing like politic, moral compass, religion because it adds entirely another layer on this.