There are some that will say they are a private company and they can do that.

And this is partially true, a company can decide to not make business with someone but they can't break contracts.

Imagine a guy and girl go to bakery shop and couple tell the baker "I want you to make a cake for my wedding." and the baker says "congratulations, you are beautiful couple". The guy hears that and says "no, she is my sister, I am getting married with my pet chicken", and after it the baker says "sorry I wont make a cake for you under such circunstances".

At this example the baker has the right to not do this cake, but he dont have to right to break the contract, he dont have the right to listen to that say he will do the cake and then few days after it say "Sorry I wont make a cake for you."

What internet companies are doing is breaking the contract, when you join some site its assumed they wont censor you under some situations they are now censoring people. But not only that, they remove your stuff, while creating some fake excuses to why they are doing that and try to hide they are doing that, so they want to trick you unto staying with their product.

But there is even more, sometimes they even make harder for you to use another product (like when patreon people censored people and after people moved to subscribe star, as a boycott, suddenly paypal stopped making business with subscribestar). So its like a baker that only make cakes using piss during the process and this baker not only will only will not sell other kinds of cakes to you but wants to make sure you eat only this kind of cake (or no cake at all).