If people are not allowed to speak openly about their Nazi opinions, they will simply do it silently between each other, creating an echo chamber.
Imagine that you're having a nice life until a black family moves in next door and turns whole area into a ghetto. Everyone around you tells you to suck it up and stop being racist. Online platforms ban you for racism. Until one day you stumble upon secret underground community of people in similar situations. Sure, some of their claims might be a little extreme, but at least they're the only ones willing to listen to your problems without telling you to shut the fuck up.