My concern with big companies deplatforming political extremists that weren't in the public eye is that it almost validates their "they don't want us saying XYZ because it's true" points. Not that their political shit has any basis in reality, but when impressionable people see that they actually are being squeezed out of the internet, it leads many of them to conclude that their other points are valid.
Right now, loads of extremists are taking to Discord and other private chats to discuss their points and recruit people. Inside those tight-knit private groups, there's no possibility of a random passerby to stop in and offer a dissenting view. They see their discussions as the absolute reality of the world. Pushing them deeper into those groups feels far more dangerous to me.