It is beyond the scope of this essay to discuss how long copyright should last. Such a determination should be made by an economic analysis of the costs and benefits of a given length. Personally, I feel very safe in saying that copyrights are way too large right now, possibly by as much as a factor of 10, but the fact that copyright is too long right now is really independent of the question should anything like copyright exist? I think a lot of the people who would simply abolish copyright entirely have come to that opinion by conflating those two questions. "The current copyright duration is harmful" does not imply "The ideal copyright duration is zero."
There are certainly others who argue for an ideal duration of zero on other grounds; while I don't buy those arguments myself, they are interesting and I respect those who come by those arguments honestly, rather then conflating the two questions.