But copyright does make sense "for a limited time". I think the big issues is that the current time limits don't make sense. Let's say that you interpret that having a government-enforced monopoly on creative works is what lets you make money off them, and that making money is what promotes the initial creation of those works. In reality, most of the market value on the vast majority of instances of several classes of works is much shorter than "life of the author plus 70 years". For example, a new hit song may sale quite a bit in the first year, a bit more over the next few years, then it dies out into obscurity. Long copyrights keep such works dead (no one will continue to publish it if it doesn't make money, and nobody else is allowed to publish it). So this is a net loss to society.
Now what what really makes sense, and feels more fair, is that if you as an author want to use my government's force to maintain an exclusive monopoly on your work, then you should pay for that service. This could be a per year fee (doesn't have to be a lot), so that if the work becomes abandoned then it doesn't become lost to society.