Copyright has obviously gotten out of hand. Even ignoring the complexities of differences among laws from various countries, which you'll have to deal with anytime you cross international lines, just within the US, copyright law has become convoluted and complex. It is no surprise that the lawyers are making a killing off helping all these authors comply with the law and protect themselves from each other, all the while increasing costs and reducing creativity.
Unfortunately, when I teach about copyright as part of a larger unit, generally the most I have time for is to briefly explain that copyright protects your creation as soon as it is put in tangible form without any additional registration or notification required and that fair use allows some exception to this rule. I guess I go slightly (but not much) deeper than that, also briefly mentioning work-made-for-hire, open source vs all rights reserved software licensing, citing your sources, plagiarism, and the DMCA. If I have time I try to at least point out Creative Commons by showing a CC search on Flickr.
Other than government-produced works, 80-plus year old works, some works where someone forgot to renew the copyright or inadvertently left off the copyright notice back when the law required either of those things, or people who specifically release their materials into the public domain, we are left with tons of material that can't be reused by anyone without a big hassle...until the GNU and CC folks came along.
Ideally, we would have much more content in the public domain, but the GNU and CC open licenses allow for more sharing of content while protecting the author's copyright claim. So would we be better off by converting these open licenses over to public domain? That is, if more works moved from all rights reserved status to the public domain, we should theoretically see an increase in creativity and a decrease in production costs, so wouldn't it follow that by changing these open licenses (which contain restrictions) to public domain (with no restrictions) we would see a similar change? I don't necessarily think we would be better off.
The open licenses provide some benefits that the public domain does not, given our current IP climate of extended-length, automatic copyright. Copyright exists, according to the Constitution, to encourage new works by granting the right to exclusive use of those new works to their creator. If the only two choices given an author were infinite full copyright or completely giving up all rights to a creation, I believe we would see less overall sharing. The reason the open licenses work is that they allow the creator to retain the rights they care about, while allowing others to use their material in certain ways. This compromise is the strength of the open licenses.
If copyright reverted to its original term of 14 years or to a model of requiring registration or notice to retain copyright, the open license issue would be moot. Many materials would quickly become public domain and we wouldn't need alternate licenses for them. I believe that many people that are willing to voluntarily apply a "some rights reserved" license would be unwilling to give up all their rights. Even the simplest case attribution-only license is important so that acknowledgement is given to the author; that is not required of public domain materials. An author is unlikely to review his or her own materials on a regular basis to decide which old materials should be released to the public domain. He or she will likely decide that when it is published. The open licenses allow the author to set it and forget it.
Should copyright law be scaled back so works enter the public domain faster? Yes. Is that going to happen? No. Would we be better off by releasing our creations into the public domain instead of using an open license? That depends. If people will actually do it, then yes. If they reserve all rights, because they don't want to cede some, then no.