The "platform" argument is based on a misreading of an American law. Whether or not someone call themselves a platform is completely irrelevant. I don't lose my right to not disseminate your speech just because I may choose to disseminate somebody else's speech.
> Wut? How does free speech infringe on free speech, exactly?
If I want to host a community for a particular purpose, but the government forces me to host the community for another purpose, my right to free speech along with everyone who wanted to participate in my community has been violated.
For example, maybe I wish to host a community for supporters of a particular politician, but the government says I also have to include the much more numerous opponents of that politician, maybe I wish to host a community for a marginalized group of people, but the government says I also have to include those who hate those people, or maybe I just wish to host a community that as many people as possible want to use so that they will look at my ads, but government says I also have to include people who make the community worse for everyone else. Regardless, the government has used force to control speech, and has in effect banned certain kinds of communities. That's not free speech.