Nazism isn’t “banned” per se, at least in the U.S. as the First Amendment does not allow for viewpoint discrimination, however repugnant a viewpoint might be. But the First Amendment does not protect against cultural, social, or other forms of non-government backlash for those who support disgusting ideologies like Nazism.

So there is no “banning” that could take place of the Zionist viewpoint, if we were to consider it on par with Nazism. By and large in the U.S., Zionism and Nazism are not seen as equally repugnant viewpoints in the cultural landscape, hence the difference in how supporters of these views are treated. Hope that makes sense.

Wtf? Is this real?