I'm all for free works and the Public Domain. The only problem with assuming that some work is free unless otherwise noted is that an entity with more resources can claim the same rights, and therefore profits, to a given work until presented with a significant challenge. A smaller entity can easily placed on a disadvantage.
If there's a public database of all copyrighted content they can't just assume without checking.
As far as copyrighting is concerned I think it's fair to require you to put some effort into protecting your works.
However free copyright should only last about 20 years after that a small fee should be required on the 21'st year and that fee should grow exponentially[1] every 10 years from then on.
If it's valuable enough to you you will pay the fee but if it isn't you will release it into the public domain.
That will prevent people keeping thing copyrighted for too long and companies like Disney could keep their stuff copyrighted for at least 100 years before the fees get too large.
If it's no profitable there's no point in keeping it copyrighted and you're just hurting the public domain by doing so.
