What is theft? The reason I ask is that for most people theft/stealing basically means taking something from someone so that they no longer have it. Copying is not seen as theft, as the person still has the original item.
I personally like the idea of Social DRM, but it comes with an expectation and acceptance that society views the idea of theft as taking an "un-authorised" copy.
I hope, and believe, that over time (decades, probably) society will come to understand and accept when copying is theft (and, of course, when it isn't).
(Charlie Stross has an old blog entry related to
the economics of ebooks and why it is broken, as well as a more recent one on
why he doesn't take money on his website.)
As for the issue of duration of copyright, the historical perspective (and the moves related to that) are quite interesting. It seems to start short after lengthy debates that indicate why it should be short, and very slowly increases the length. One thing that has intrigued me, is the difference in duration between copyright and patent life...