I have previously blogged about a problem known as dynamic time inconsistency.
This is exemplified in the patent issue. No patents discourages innovation, since inventors have little to no incentive to create. Infinitely long patents prevent society from reaping the full benefit of invention. The optimal policy is to guarantee inventors patent rights until the moment of invention, and then yank out the rug.
This, of course, is not a viable long run strategy. However, a PhD candidate at Cambridge, Rufus Pollock, has calculated the optimal length of patent protection. 14 years, as it turns out. Obviously, as economics is wont to do, subject to more than a handful of assumptions and estimates of certain parameters.
Still, 14 years, to me, feels a lot better than life+70.
Such calculations also figure into Schumpeterian growth theory (aka creative destruction), which is something I like.