> But they are breaking a norm

Media companies selectively choosing what to publish has been the norm since forever.

My local paper won't publish libellous comments I may write against a particular person whom I hold grudge against. And my local TV station wouldn't show a pornographic commercial that I thought would be hilarious to see.

Private media companies ultimately answer to their advertisers and most of them simply don't want to be associated with inflammatory or socially unacceptable content.