Suppose you have enough resources to try to do it "right". How do you moderate in a way that's globally fair? There is disinformation (which should be moderated), but there are also legitimate disagreements (which should not). Even facts themselves are often open to interpretation, and people don't argue in objective terms.

The degree of nuance leads me to believe it's just impossible to do at commercial/global scale (though I would agree it could be done better than it currently is).