It's not necessarily a contradiction to want anonymity to be piercable by a court's subpoena (which would force NFS to divulge their records), but not by anyone who can send a convincing looking letter. A hosting service which makes a point of protecting its members in the event of complaints, even if this is intended for the type of stuff you'd classify as "free speech" (which is mostly, though not entirely, legally protected in the U.S.), is likely to attract a lot of users with various less sympathetic purposes; whether or not you think any particular such purpose should be allowed on the Internet, they have the right to think it shouldn't.