You're not intending to, but by giving the government the ability to regulate political speech you are.

And yes; telling Twitter what they can do with political speech is governmental regulation of protected speech. You're giving the government to decide what forms of protected speech get extra special protection, which is a form of regulation.

> I am suggesting that Twitter might be a monopoly, and subject to the common carrier doctrine, on "being the watering whole for the entire media/political class".

So, I can declare any company a monopoly if they have cornered a specific user base, no matter how vague? Is Slack now a monopoly because they're popular in tech offices? Can I regulate declare Reddit a monopoly for sports fans and regulate it as such?

What is the general principle that will decide whether or not a company should be regulated as a monopoly? And how in the world do you define the "media" class in order to regulate companies like Twitter?

Only 22% of Americans use Twitter daily. That is not a monopoly, period.

> but I think we can all agree that you can't just start your own Twitter and have the same unique position of political influence.

Sure, but that's no argument for an expansion of government power.