Invariably someone brings up "Free Republic."
Free Republic is a club. It is also not a significant carrier of public speech. It is a private club that isn't open to the public, and it very likely has less than 1 million users.
Also, you need to understand where this existing status quo is going to go if it is allowed to remain as it is. It's going to slowly move the entire nation into totalitarian socialism.
Allowing Google, Facebook, Twitter and other people to control public speech is an existential threat to the nation. If we let these existing conditions continue, we will lose our country.
How would you quantify and limit the "significant carrier of public speech?" Just claiming a group is a club or is too small does not seem to be a practical exemption to an effort to stop censorship on social media platforms.
The Supreme Court used a very broad brush to end segregation. Enforcing Free Speech rights on fb and twtr seems like another dangerous slope for us with the chance of equal time provisions and the like. As in, be careful what you wish for.