Taking down a Nazi website creates no onerous obligation to police the entirety of the web. Addressing only those sites which rise to prominence admirably moves us towards a better internet and society.
Of course, it's only one high-profile incident and it should be possible to successfully argue that you (namecheap) only act on this policy when information about the violation actively reaches you as a passive observer. But you are then playing from behind so it's still not as if this action carries no potential future liabilities.
If a website that incites violence can be taken down because of a single violence-inciting remark, then people will just post violent remarks on their enemies websites and proceed to get them taken down. As an administrator, whether of a domain, social network, forum, or services on other layers of the Internet, it's unreasonable to be held responsible for every single thing done by your users. That doesn't mean you have to let them do anything, but when a problem occurs, the first step should not be to start taking down websites and servers, instead of looking for a more reasonable solution.
They need to find a registrar whose market position is built on taking a stance. Namecheap ain't it.