My unpopular opinion is that social media is simply inherently incompatible with human nature. I don't think it's anyone's fault per se. It's like heroin in the sense that it doesn't matter how you distribute it - it's going to cause harm because hijacking our reward systems is the reason we use it in the first place. If you modify it so all that goes away, then what you're left with is water - and nobody wants that.
I don't know what the solution is, though. I don't think banning it is a solution, but I'm not sure how to square the harmfulness of it. It's not just kids it's bad for - it's everyone. And yeah, there are degrees to it - perhaps Lemmy is objectively better than an algorithm-based message board like Reddit, but something being better doesn't make it good. A non-toxic heroin that you can't OD on is also better than the alternative, but it's still going to be harmful. It's an arbitrary line we collectively just decide to draw somewhere - even though you could argue infinitely about nudging it one way or the other.