I believe that copyrights should be infinite. I do not see any reason why a copyright should expire afters a certain amount of time. I think that if somebody is responsible for creating something, that person or persons should have the legal rights to its creation for eternity without it expiring.
Intellectual property including copyright and patents only exists to serve the public interest. It only exists in order to foster innovation, to provide an incentive. Therefore not only should it expire after a certain time (which in the case of copyrights it expires after a period of time after the copyright holder's death) in the case where the public interest requires it the government should use eminent domain to release it to the public domain. Certain automotive technologies that companies patent and then not use just in order to hold back innovation come to mind.
At some point, copyright laws should be allowed to expire, because the public benefit of the technology outweighs the descendants' right to make a profit. Once the people have been allowed to earn a reasonable profit on what the technology is, we should be able to use it, for example when a prescription drug can be offered generically much cheaper.
Copyrights are important in our world because they protect the creator of properties. However, these copyrights should expire after a certain amount of time because there is no reason to continue the copyright far after a persons death as they can no longer gain profit from the sale of their property.
No, copyrights should not be indefinite, because at some point they have transferred so many times they are no longer valuable. At some point, a work should become common so that it can be used and improved on. It is nice to let other companies make a generic of a drug, or make a work public so that it can be more popular.
It's a good thing that copyrights expires. Just because you thought of a great idea, doesn't mean that people for years to come should be able to exclusively profit from your work. It provides generations in the future access to free content because it will be things that aren't necessarily popular in the that.