No such thing as neutral space

it may not be intentional, but

They can suggest similar [communities] so it can't be neutral

My guy, what? If all you did was look at cat pictures you'd get communities to share fucking cat pictures. These sites aren't to blame for "radicalizing" people into sharing cat pictures any more than they are to actually harmful communities. By your logic, lemmy can also radicalize people. I see anarchist bullshit all the time, had to block those communities and curate my own experience. I took responsibility and instead of engaging with every post that pissed me off, removed that content or avoided it. Should the instance I'm on be responsible for not defederating radical instances? Should these communities be made to pay for radicalizing others?

Fuck no. People are not victims because of the content they're exposed to, they choose to allow themselves to become radical. This isn't a "I woke up and I really think Hitler had a point." situation, it's a gradual decline that isn't going to be fixed by censoring or obscuring extreme content. Companies already try to deal with the flagrant forms of it but holding them to account for all of it is truly and completely stupid.

Nobody should be responsible because cat pictures radicalized you into becoming a furry. That's on you. The content changed you and the platform suggesting that content is not malicious nor should it be held to account for that.