A business doesn’t have to be a monopoly per the current legal definition for it to be subject to regulation. We can simply require social media companies to accept all customers. We can make political views a protected class that prevents denial of service at businesses in general. We can treat these tech companies as utilities because they operate the public town square. There are numerous routes for us to fix the current situation, where a small number of employees controlling these companies with billions of users, can become the sole arbiters of can communicate and what they can communicate. It just requires that we start talking about it, educate people about the problem, and build political will.

We probably can't "simply" do that, in that the Constitution is a document with actual meaning.

I would also note that there are existing platforms that effectively make political views a protected class. It turns out they are not very popular, because most people don't want to hang around with people for whom the 14 Words are an important political view.

In practice, a platform can either have haters or the people they hate. Insisting a platform accept all the haters means you're guaranteeing the people they hate will go elsewhere. That's why Twitter has moved away from the sort of policies you favor. As an example, look at when Milo Yiannopoulos led a wave of racist abuse toward Leslie Jones. Twitter had to choose between keeping her (and a lot of her fans and people who just don't like open racism) or Yiannopoulos and his fans.

So the notion that we should override the Bill of Rights to make Twitter platform everybody is not only anti-freedom, but also won't in practice work. If somebody doesn't like Twitter's rules, they should do what you're doing: post somewhere else. There are platforms ready and waiting to take them.

How do you think antitrust laws were created in the first place?