I am an American who thinks a lot about the entire scope of the First Amendment. Of course the First Amendment is not just, as written, an injunction on Congress, but also a statement of the ideals of a free society. It includes the right to freedom of assembly (by name) and association (not by name, but by clear caselaw), and Namecheap, as a private business, has the right to associate or not associate with whomever they want. A society that obligates a private business to provide business to everyone, whether by cultural norm or by Congressional law, is not a free society.

There are a couple of protected categories, as stated both by the Constitution and by society's norms. Being a neo-Nazi is not one of them.

The site's perfectly available. There are multiple links to it in the thread. No one's right to speech is being infringed.