I've wondered this myself. Platforms could censor illegal material as required by law, then leave the gray areas to users. There's a pretty big technical challe

I've wondered this myself. Platforms could censor illegal material as required by law, then leave the gray areas to users. There's a pretty big technical challenge, though, because instead of training a single one-size-fits-all algorithm, you suddenly have to train N algorithms, where N is the number of users on your platform. In order to scale, this training may have to be done on the client. But in addition to the technical challenge, I doubt these platforms want to cede the enormous power they have over information distribution. Right now Twitter can flex on the president of a global hegemon, which is crazy power. Why would they give that up?