Lengths just have to be reasonable, comparable to time in production (median of salaried employee-hours / median # of employees over the period) of the average

Lengths just have to be reasonable, comparable to time in production (median of salaried employee-hours / median # of employees over the period) of the average item in a class. The vast majority of the private value is captured well within that time. It also keeps people honest and discourages rentseeking that isn't tied to labor. Ownership of intellectual property still matters, but right to copy&modify shouldn't last that long. It isn't hard to imagine another system of IP rights that provide value to the creator but not to the expense of society. Disney used public domain to build it's foundation then pulled up the ladder. Disney's market cap is lower than the damage longer copyright has caused, it's already been trillions, hundreds of trillions looking into the near future.