Would you replace copyright with "terms of use" or something in a contract with the performer?

I see the value of copyright (or other intellectual property protection, such as the "terms of use" I mentioned above) in this case, for two reasons.

First, the value for the creative doesn't scale. Suppose a conductor commissioned some music to be written for six summer evening performances. How should the music writer value the work to be written? The negotiations would probably consider how much revenue the performances will generate, and result in a (presumably) fair compensation for the writer.

But suppose the conductor, after the piece has been written, uses the it for eight performances? Or switches to a much larger venue that generates much more revenue? If you don't allow for a way for the writer to be fairly compensated you run the risk of not being able to attract good writers to the field. We could argue that geniuses and top talent would still be there, but it would be difficult for merely talented to make a living (or for the unknown to start out).

The second reason I see is to protect the reputation of the writer. John Williams is a brilliant composer who has written some of the best and most-recognizable movie themes. He wrote, for instance, the theme for the movie "Jaws."

Suppose someone took his music and used it as a soundtrack for a movie that he found very distasteful (a porno, or a movie advocating the rise of the Aryan Nation, for example). He would then be associated with these other ideas, even against his will. You could argue that his ability to use music to conjure emotions could be used to rally people for causes with which he vehemently disagrees. Copyright can help protect against that (but can't completely stop it, of course).

If it were really necessary (though I am unconvinced that it is) a royalty system could likely be emulated in a society with no copyright with contract and corporate law.

Write a song for Metallica? Sell it to them in exchange for some amount of cash up front, and partial ownership in the company that is selling that particular album/single/whatever.

Clumsy perhaps, but if big money is involved the overhead should be minimal.

The problem with selling to Metallica is that you are selling something that you don't "own." Said another way, the value changes when you can offer exclusivity. It'll be worth less to the company producing the music if someone else can (legally) take the music also.

Now I wouldn't cry if the era of multi-million-dollar entertainers is over, but I think that it would be a mistake to throw all copyright out. Rework it maybe, but keep the idea that mental creations are assets just like physical creations are. The concept of copyright arose because there appeared to be a need to protect those rights when that protection was absent, so I would be very hesitant to throw the baby out with the bathwater when it comes time to reexamine our IP laws.

For me, the SOPA/PIPA issue is about due process. Taking a site offline can be damaging in ways that may be hard to quantify, so the standard of proof should be pretty high IMO.