I think you should be free to say what you want and to think what you want, I also think a privately owned space has the right to remove people who are saying things they don't want in that space.
Here are three examples:
(1) You own a bar and someone comes in and starts calling your patrons racial slurs, can you throw them out?
(2) You start a social media company and somehow a large contingent of your initial user group turns out to be a hate group. Shouldn't you be allowed to remove the group and their hateful content? Do you really want to be REQUIRED to leave it on the site unless it is breaking a law?
(3) You start a social media company and it grows to the size of twitter. Your site is one of the most visited sites on the internet, and is getting overrun with hate speech. Don't you want to be able to remove that?
Are you fine with one and two but not three? Where's the line? If you want to argue that Facebook and Twitter are utilities and should be regulated as such, what do they get in return? Don't forget, utilities are often government sanctioned monopolies or near-monopolies in "exchange" for all of their regulation.