I'm in medical research. Do I think antivaxxers should be able to publish in medical journals? No (unless they performed an experiment that passes peer review, etc).
Do I think they should be able to run their own websites, have nonviolent meetings or rallies without losing their jobs? Yes, I do. Even though antivaxxers are doing far more harm than neo-Nazis are.
Also, "scientific/academic consensus" and "rationality" are not synonyms.
That is literally what OP is about.
Now if it were the ISPs handing this ruling we'd be on the same page, but it isn't. There's no freedom of speech argument for "right to demand services without restriction". Same way a restaurant will turn you away if you show up with "no shirt, no shoes". Namecheap is using the freedom of speech of it's leadership in saying "Nazis and other groups that incite violence are not groups we want to host".
Right for service totally without restrictions, no, but "viewpoint-based discrimination" or other types of discrimination are a separate legal category for a reason. "Shirts and shoes required" is different from "whites only" (or, for that matter, "liberals only") on a restaurant door. We allow the former but not the latter, and I think that's reasonable.