That's a good answer to this. They should be responsible for what the algorithm decides to inject into people's feeds, when they are acting as a publisher.

If they don't have enough resources to review the outputs from their algorithm, then to bad, just show posts from friends only.

There will always be false negatives. Is one false negative enough to drag them into court? So every website on earth will just have that one moment where they accidentally promote (or don't actively de-promote) something toxic, and they'll get to go to court over it. I wonder how much Twitter will have to charge now. $8/mo isn't going to cut it. More like $80,000/mo

They don't promote it blindly. They promote it knowingly.