Gab has a bunch of wacko posts as well. I suspect some of them are paid operatives of the Swamp. Given the intense efforts of the left to wipe them out I’d be surprised if they were not any such agents.
Yes, they’re a platform - they provide a forum for people to express views. Did these people act on the things they said? If so then they committed crimes but just saying things on an open platform is what the protection is for.