Similar regulations have existed in the past (common carrier and the fairness doctrine, for example) without giving the government the power to "declare which ideological believes are and are not protected from moderation".
The fairness doctrine was only constitutional because there were a limited number of channels (Red Lion Broadcasting Co. v. FCC), and it was impossible for anyone else to create one due to FCC regulations. I genuinely doubt that it would be constitutional today with cable television, let alone the internet.
I'm not proposing that we reestablish the fairness doctrine, just using it as an example of similar government regulation in the past that didn't have the disastrous effects you predicted.
But since you brought up the limited number of choices, I would like to mention that we find ourselves in that situation again today in the smartphone and online video markets, although for different reasons. And that's relevant because regulation is only necessary when the free market fails to provide the choices and freedoms we expect.
