However unrelated statements, even very politically incorrect ones, should be outside it’s remit. If for example someone was a virulent racist on twitter. That’s arguably a bad thing, but those statements are unrelated to the project and should have no bearing on contributions to it.
(Now that’s going to be an unpopular sentiment. Downvotes ahead.)
Does "shut up and hack" apply to telling them to keep their racism to themselves?
(I realize you didn't say anything about racism, but you replied supportively to a comment about it, so I'm not sure where you stand.)
If that's really true, doesn't "shut up and hack" apply all the more? If you really cared about the code, you could keep your political opinions to yourself.
(Also, this is precisely why many codes of conduct define the exact harms they care about - so racism is an excluded harm, but, say, making Hans Reiser feel bad about being a murderer isn't. If you're a fan of racism, you might use this as an indicator to avoid the project and find another one, or fork it under the license.)
However on forking I do tend to agree. There appears to be an audience for projects with less controlling, or less ideologically intended rules. These projects should be formed and developers should make their own choice between them.
I do agree on the other hand that digging up 30-year-old Usenet posts would tend to just get everyone in trouble and a code-of-conduct process should ignore them, or at most provide ample opportunity to distance oneself from those statements and then go with what's said today.
My preferred solution is to make sure the party handling the code of conduct process is someone who seems level-headed and likely to use their judgment well. It means you move away from codified rules, but it also means rules can't be gamed. For Linux the enforcement body is the Technical Advisory Board, which I think is a little weird precisely because it's a technical body and not necessarily a good-at-people one, but we can see how it goes. For small projects the enforcement body is typically the project founder, and if you don't think the founder will handle things reasonably, no code of conduct can make them trustworthy.