Julian Sanchez wonders why copyright terms are so long, and offers a retromaniacal speculative theory: it's a form of "protectionism against the past":

"Insanely long copyright terms are how the culture industries avoid competing with their own back catalogs. Imagine that we still had a copyright term that maxed out at 28 years, the regime the first Americans lived under. The shorter term wouldn’t in itself have much effect on output or incentives to create. But it would mean that, today, every book, song, image, and movie produced before 1984 was freely available to anyone with an Internet connection. Under those conditions, would we be anywhere near as willing to pay a premium for the latest release? In some cases, no doubt. But when the baseline is that we already have free, completely legal access to every great album, film, or novel produced before the mid-80s—more than any human being could realistically watch, read, or listen to in a lifetime—I wouldn’t be surprised if our consumption patterns became a good deal less neophilic, or at the very least, prices on new releases had to drop substantially to remain competitive.

If that’s right, there’s a perverse sense in which retroactive extensions for absurd lengths of time might actually, obliquely, serve copyright’s constitutional imperative to “promote the progress of science and useful arts”: Not by directly increasing the present value of newly produced works, but by shrinking the pool of free alternatives to the newest works... If that’s true, though, it’s not enough in itself to justify the longer terms: The question is whether the marginal new content is actually worth losing universal free access to the older material. For reasons unclear to me, there often seems to be an undefended assumption that more newer stuff, whatever the quality, outweighs wider access to existing content at any conceivable margin. I’m not sure how you’d go about quantifying that, but it strikes me as wildly implausible on face."