So in many ways, this is the crux of the problem. You have interest groups and politicians lobbying these firms to self-regulate, which in my assessment is generally good. I think the best argument for regulation is under the UDAP standard, Unfair or Deceptive Acts and Practices. You could claim that these companies are platforms for such so any new standards to filter content need to go through an Administrative Procedures Act-like review. Facebook’s new Oversight Board is a good starting place but it is reactive thus not doing enough.