requesting info on a real, existing user on illegal-in-USA.ru
-> GET /users/real-user-name HTTP/1.1 Host: illegal-in-USA.ru
<- HTTP/1.1 451 Unavailable For Legal Reasons
requesting info on a fake, nonexistent user on illegal-in-USA.ru
-> GET /users/no-such-user HTTP/1.1 Host: illegal-in-USA.ru
<- HTTP/1.1 451 Unavailable For Legal Reasons
If the .ru site sent 404s for nonexistent users and 451s for real ones, you'd be able to gather potentially useful information. It's like if I go to bad-porn.com and type your email into "forgot my password", it should neither confirm nor deny the existence of your account, simply tell me the request was received. In any event if delivery of the requested resource is legally prohibited, why would I go to the trouble to determine whether the resource exists?
A final analogy: 10 year old enters US gas station: "Have you Marlboro 100s, menthol?" gas station attendant (without checking whether or not he has this particular brand/style of cigarette): "get out of here, kid. [HTTP/1.1 451 Unavailable For Legal Reasons]."
A final analogy: 10 year old enters US gas station: "Have you Marlboro 100s, menthol?" gas station attendant (without checking whether or not he has this particular brand/style of cigarette): "get out of here, kid. [HTTP/1.1 451 Unavailable For Legal Reasons]."