Okay, let us discuss if the database is copyrightable in the USA, Australia, Canada and the European Union for the hell of it.
First of all, USA. Oh boy, this will be the most controversial passage. It seems that there's a strange consensus that the Feist Publications Inc. vs. Rural Telephone Service Co Inc. case automagically means that freedb is not copyrightable in the US. I argue it _is_ due to several factors, such as originality and innovativity in the way data is organized and extras people have entered which constitute original, creative work. Freedb is different from Rural's phone directory in that the way the data is organized is not dead obvious and it contains information that is easily argued to be original and creative. Both of these are different from the main points of the US Supreme Court ruling Rural's database noncopyrightable.
Stripping all of the creative work and abandoning all of the current organization of the data may or may not be an option to free oneself from the obligations of the license - you'd probably have to be sued to find this out conclusively. I agree that the discid may be a redundant notion in well-organized real databases, but it was an innovative solution back when the original author of xmcd had to come up with a sensible way to organize the data in a flat database so that it would be easy and fast to find entries matching the discs in the user's CD drive without scanning through the whole database (with time the sensibility of the design turned out to be questionable for what the database ended up being used for, but that's beside the point). Thus I consider the notion of a discid definitely innovative, creative and original.
Unlike in the US, in Australia, Telstra's database was ruled copyrightable alone by the hard work required to construct it without even having to consider the creativity and innovativity aspect further. The case went to Full Court of the Federal Court which ruled unanimously for the copyrightability by stating that the datasebase has originality by virtue of Telstra obtaining and listing the data. The special leave to appeal the Full Court of the Federal Court decision was denied. This was a polar opposite of the US decision and should make it quite difficult to argue that an Australian would be allowed to turn the freedb database into Public Domain as it not only contains facts laborfully gathered and made available by the community (which appears to be sufficient for copyrightability) but also an amount of creative and innovative work.
Canada appears to be somewhere in the middle (CCH Canadian Limited vs. The Law Society of Upper Canada). I haven't read up on it enough to make even a semi-informed opinion. However, I don't think things are as clear as topham seems to make them to be. I will read the relevant documents in detail tomorrow.
AFAIK the Europan Union Database Directive should make it difficult to argue that freedb is not copyrightable in the European Union. This is as much as I'll say about it, as I have not read up on its details too much yet. The relevant directive and law implementations are publicly available for everyone to read, so I'd appreciate if someone could shed some light on EU's side of things.
I would argue that making the freedb database PD even in the Western countries will be a hassle at the very least and may be considered copyright infringement in some legislations. In any case, I would advise against it due to the effect on one's reputation it could have: releasing the database into public domain would likely be followed by companies making proprietary versions of it, which a lot of people would not like. I find the GPL, while awkward in the context of a database, something that protects the freedb database from corporate interests. If it absolutely must be relicensed (assuming it were allowed), then something else than PD should be used IMO.