Well, but they can use the internet. It's just that people who don't want to hear them (which is most people) won't hear them using the internet, and that is okay and not a restriction of free speech. They can communicate freely with people who care about their viewpoints over the internet, with people who want to communicate with them, but not on the platforms whose subscribers don't want to communicate with such people.

The right to free speech doesn't include the right to force your speech on people who don't want to listen to you.