In those cases the solution isn’t to force those companies to moderate their content differently, but to prevent them from becoming de-facto monopolies.

The popularity of Twitter, Facebook, Amazon and Google’s core products isn’t the issue. The issue is that any time a successful competitor comes up, they can just buy them out.

Imagine if Facebook wasn’t able to buy Instagram, and it had survived as a competing platform?

There’s no need to apply the concept of “free speech” to private companies. There is every need to regulate monopolies so that a handful of tech giants don’t have the power to effectively suppress content across the majority of the outlets people are using every day.