Not sure where to start with this. In the interest of keeping it short, your logic simply doesn't work. Yes, you can choose not to do business with them. However, FB, Google, Twitter, Apple, Microsoft, Amazon, they literally have technology market cornered.You are WAY off. Twitter, Facebook, et. al are all for profit businesses that sells advertising targeting users based on their behavior on the internet. As businesses they are allowed to enforce terms of service which EVERYONE signs as a condition of using that platform... they give themselves, in these terms of service, the unilaterally right to change conditions 'at will'. If you are a user and you don't like this, then don't sign the terms of service and use it. They are not making 'publisher' decisions, they are enforcing terms of service, which is their right to do. They have never claimed that they are a publisher.
If you as a business want to be led around by the nose by SJWs, that is YOUR RIGHT to do.... then you get to suffer the consequences of your actions. There was a business that decided to start charging men more for coffee because of the mythical wage gap, that coffee shop is now going out of business. There was a not-for-profit business engaged in a worthy cause I was involved in, then got full of themselves and some SJWs decided it was a good idea to have an event where white people had to pay more.... because 'white privilege' ... Well now I don't have anything to do with them and neither do a lot of people.
You only become a 'publisher' when you start creating content. Facebook and Twitter, et. al DOES NOT create content. The only issue with social media platforms is if they have an obligation to inform the public of the veracity of claims made on their service. Personally I think they do... they should not limit what people post and say, but I believe it is appropriate for them to place context on what is published on their platform. So if some Russian troll posts a 'story' from a mythical service called "American Freedom Press", detailing that Hillary Clinton was running a sex slave operation out of a pizza place, I think Facebook or Twitter can and should detail exactly where the story comes from... then people get to decide if they want to believe it. No one can police what people chose to believe, and there was a butt load of really stupid sh!t that finds it's way on social media that people believe because human nature is that we make emotional decisions about things, then look for evidence that justifies their belief. Few people rationally evaluate everything they see.
People have the right to say what they want... even if it made up BS. Private companies have the right to set conditions on doing business with them.... AGAIN. If you want to exercise free speech, and you can not find a platform that is willing to host your content, then go create your own service.... really it's not that hard. You can go out, buy a server, become an ISP, hire a developer and you are off and running. Your reach will not be as good as broadly used platforms, but the right of free speech does not require others to listen or read what you have to say.
Yes, I suppose if you had some capital, you could start some competitor but that is extremely unlikely to rise to any sort of level that would be real competition for them, to give say for instance, conservatives or libertarians, another choice besides their platforms. Not only do they have a war chest that would simply outlast you, no matter how poor their business model or product is and no matter how much better your product is than theirs.
Do you honestly think, and I've ready many an article on the shady business practices of Microsoft just for one, that these companies would ever let you get to the point where you could compete with them? Microsoft has literally gotten into a genre of business to simply put out of business another rising company that they thought might be competition for them down the road. How would you ever undo the stranglehold that they have on the market at this point? Our country's fortunes literally rise and fall with their success at this point.
At this point, the horse is out of the barn and they now control the market, for better or for worse. And they lean largely liberal, fascist, communist mindset. Compare what they do and what they want to do, you see a perfect implementation of this in China's social credit score. Do you really want that here? I hope your answer is no. But that's what they want to do.
These companies want it both ways. They want you to publish your content and they want to control what you say/do on their platform. They literally have items in their terms of service that give them control over your content once you publish it. However, if you are a company, business, organization and you want to reach people on a wide scale, it's going to be pretty much impossible without using their platform at this point. And to your point, I suppose they can change their terms of service at a moment's notice but with the reach and power of their platform, that is simply not manageable by most people or businesses, that can literally ruin them at a moment's notice. Youtube invited content publishers in to create content to make them great. They didn't say "Oh, we only want liberal opinions on our platform", "We only want cute puppy and kitten videos on our platform", they invited everyone. Now that they have all the control and money, now they get choosey, that's wrong.
These companies want net neutrality, in the guise of fairness and a level playing field for everyone, but what they really want is the control. Make no mistake about it, they're grabbing for even more power and it would appear by your post, that you at least tacitly support them doing so.
I'll finish this up with, if you want to start letting people and companies discriminate on the basis of political opinions, race, religion, orientation, there's not many people, besides your standard SJW, that will be allowed on any of these platforms and the web in general. A site like this, don't worry, they'll eventually get to you and your opinions on here, most of which would fall short of the SJW ideal mindset and then I guess, you're gone. But I suppose if you want to start letting people discriminate, you can do that but you can't say, SJWs, you can discriminate against western culture, whites, males, christianity, but everyone else, that usually means white males, you can't be discriminating at all. When you start applying these cultural norms, values and other aspects of morals and ethics, it usually leads to ugly outcomes for society in general. See the bolshevik revolution, mao's takeover of china, stalin's purge of anyone who looked at him the wrong way.