It seems there are two contradictory statement here, at first it is pointed that Mixers are not illegal which is very true, So what other law of the country are the staffs meant to follow?, because if there are no laws there will be no violation, So it is obviously not related to where the forum server is located nor has anything to do with staffs who are residents in the US, If it was so the restriction would have been made public.
Maybe I didn't explain myself well.
First point, I didn't say that the moderators were employees or that they were all from the US. I say that before the authorities they can be classified as such, especially if they receive something (I don't know if they do).
Another thing is the fact that mixers are not illegal, but in a gray area of the law. In fact mixers are not illegal, they can exist. But according to the US authorities must comply with some rules. Note this interesting article from Coindesk, in part it says:
In the U.S., the Financial Crimes Enforcement Network (FinCEN) considers mixers to be money transmitters under the Bank Secrecy Act (BSA) that need to be registered and meet certain requirements. Chainalysis, however, noted in its report that it is “not aware of any bitcoin or Ethereum mixers currently following these rules.”
That is, the existence of mixers is not illegal, but they have to follow some rules. Rules that no one seems to follow. This may give the impression that they are illegal. Well, those who do not comply with these rules are illegal. But, will Bitcointalk have to verify this? Logically not, it is the authorities who have to verify.