Please pay your forefathers for each word you use, each thought you have and even each invention you make for their share of what you reused.

As a first line argument: It's not that you are owed anything (as tshaddox says, it only applies to things already shared/published), it's that you do not owe a due to others.

As a second line, I would say that yes, if you are making money off of things you share, then society deserves the right to freely use and share it (say after 20y), even if you put DRM on it (shouldn't be a thing) and even if you didn't originally publish the source code or manuals and tools. Though compulsory requirements should probably be limited as a fraction of sales.

> who is really harmed when the author of a book retains the rights in perpetuity?

Anyone that wants to make (or accidentally makes) derivative works based on that work. This is especially apparent in the music industry.

Write a story about a prince waking a princess with a kiss an you run the very real risk of getting sued into oblivion by Disney.

We, the public, lose out on creative works because creative folk have to be VERY careful with how they approach art to try and minimize their exposure to lawsuits.

Very similar to the harm done by software patents.

Who is harmed? Creators. Consumers. Anyone who ever pined for access to something out of print, or in a vault, or otherwise squatted on for no productive reason. Anyone who ever had to guess what they could sample or what they could not; what would be legally considered derivative of some decades-old musical expression (many of which resemble each other superficially) and what would not.

> I don't own any copyrights - probably never will

Actually, you do own lots of copyrights. For example, you own the copyright on almost every blog post that you made. (The exceptions are things like lists of facts.) You own the copyright on every picture that you've taken or drawn.

> why am I supposedly owed the right to use something for free that someone else created after some arbitrary amount of time

That's the natural default. If two people don't interfere with each other's happiness, then there is no copyright. You don't need a right to copy, the owner needs a right to stop you from copying.

Why are they owed the right to a government-enforced monopoly?

Well, xyz there are good reasons but also those reasons make more sense with a time limit.

It's antithetical to the very idea of culture. Humans have been modifying and retelling stories since before the dawn of civilization. Imo, it's profoundly immoral for the state to restrict ownership of culture to its creator for such a long period of time. Some degree of copyright is necessary to create a financial incentive for new works, but the currently length goes far beyond that.

You’re never owed the right to use something for free that someone else created. They ought to be able to keep it to themselves if they want.

If they keep it to themselves then copyright won't matter.