People who wish to discuss their neo-nazism can go open their own forum wherever they wish, at their own expense -- once the government stops them, we have a problem (assuming they're not actively violating any laws, etc). No one is obligated to host that content, and people who choose to host or continue to host that content are active participants in that behavior. Silence is not complicity -- knowing, and choosing to be silent, clearly is.
Of course, no hosting provider would be obligated to take their money to host them, and any that did would presumably be seen as active participants in their behaviour if they continued to do so, and the same with upstream providers of internet connectivity. So unless someone is willing to take a stand and host that content even if they're seen as complicit for doing so, then no they can't open their own forum anywhere on the internet.
Which wouldn't be so bad if neo-Nazis were the only ones affected, but sadly they're one of the groups least likely to be driven off the internet this way.
