Not so serious subjects (I prefer to relax while being on the fediverse :) ). Anything related to Facebook / Apple / Nintendo / Disney is almost always filled with comments full of hate. It is much easier to find good communities for that on Discord for example.
See, in the past, I used a lot Twitter to keep up with news about my interests. It was easy to filter out bad users by banning them, and following more « positive » people. I left when it became « X » because I had less interactions and much more ads (probably a consequence of letting users pay to gain visibility). I hoped the fediverse would replace it.
In a sense it worked, because I get a lot of news. But now, I am worried to read the comments or even comment myself because people are most of the time not kind at all. More specific communities have not this issue, but the fediverse is so small that you are forced to be part of more general communities and face the general harsh talk of most people.
I think it’s even more common among more general communities. But even niche communities like retrogaming can be like that.
Just to give a concrete example, I have seen a post about a pretty cool mod on Zelda ocarina of time where they integrated Pikmin, it has 50+ ups, and a single comment saying they can’t wait for Nintendo to shut it down. What’s the point ? And I see this more and more. It’s not the minority but the majority of the replies I see on such posts. It’s not healthy at all.