Alphax said:
Google has SafeSearch - and how many millions of people use Google?
I agree. If we do have server-side filtering, we should use the highest level of censorship as a default so that nobody can complain that they didn't ask for what they got (otherwise, why bother doing it?) It should be possible to override this by setting preferences and obtaining a long-term site cookie, without having to log in. This would make Wikipedia's behavior similar to Google's.