All these laws are doing is encouraging people to do this in order to be "edgy", to be a "rebel" and show that they're not going to "be part of your system, man". Having something as simple as saying dumb things be outlawed makes people only to want to say dumb things more. As a fan of comedy, I can tell you flat out that all the 7 Dirty Words banning did, was encourage people to use those 7 dirty words.
If you made it legal, much of the support for these groups would most likely wither and die. They'd grow increasingly irrelevant with their main source of conflict evaporated. People would be able to look at them, and see that nobodies stopping them, and question how these people can claim to know some secret nobody else wants known, when nobody has come to stop them saying it. Stormfront was mentioned, but stormfront itself not only has no power or sway, but its also a very small group of people, if I'm not mistaken. And of those people, most are assholes who wouldn't do anything in real life, and only complain on the internet to make themselves feel important.
As for /pol/, I think many of them do this just to troll. Its a sensitive issue that rustles many people jimmies so they do it. If people didn't give them attention with this holocaust stuff, they'd move on to the next horrible thing to say in order to make people hate them and shower them with stuff to talk about.
Trying to relegate dumb things out of the world, especially by forcing people to do it, only has ever made them want to do that dumb thing more. You won't get more people jumping off a cliff, then if you put a sign up asking people not to jump off said cliff.