Hitch,
I hear your pain about this discussion. There isn't going to be an agreement between us, and I'd like to describe why, in detail.
The value of work:
You state that an author works as hard as anybody else. No arguement, they do. Do they work harder than a heart surgeon, an inventor, a 24x7 on-call computer programmer, or a police officer or a EMS tech? Ah, now that is a more interesting question. You have great difficulty convincing me that authors do work <harder> than those other sorts of labor.
What is the value of their compensation? You state the speculative nature of their work. Maybe it pays off, maybe it doesn't. Therefore they need greater incentive. Why is what they do any different from any other entenpreneur? If I build a successful business, I have created an ownership in that business.
Where does this split from the copyright concept? Under normal business circumstances, anybody else is free to build an exact replica of my goods or services offered by my business. The only thing that might stop them is if they infringed on existing patents or trademarks. But patents only last 20 years, and trademarks only last as long as they are used.
So if I wanted to build exact replicas of 1957 Chevrolets as a business, there would be no patent constraints (they would have all expired) but there <would be> trademark constraints. GM still uses Chevrolet as a trademark. So my replica 1957 Chevy couldn't use any GM trdemarks on it. If I decided to build replica 1953 Hudsons, I could use all the Hudson trademarks, as they have been abandoned for decades. (Trademarks are only maintained through use. Stop using them, they stop being valid. However, your judge (like your mileage) may vary...)
However, by law, I can't build an exact replica of a work under copyright. That's what copyright is for. It is a granted limited monopoly, by a society who does not think monpolies are good things. It is not, repeat <not> property, no matter how many times people want to call it that, in order to claim the benefits of real property.
That's where the difference between being a typical enterpreneur and being an author occurs. Competition. An entenpreneur has exact copy competition risk, a holder of a monopoly does not, <for that monopoly>. It may (usually does) compete with other monopolies for the same general market, but it has no competition for it's <particular> monopoly's market. That is something that no other entenpreneur, or other form of labor has.
Is it justified, and if so, for how long?
Copyright, it's causes and consequences:
Copyright first came into existence in England, in 1714, with the Statue of Anne. It granted a monpoly of 14 years, flat. The purpose was to encourage new creative works of writing. Unsurprisingly, it succeeded.
The US embedded copyright and patent monopolies into the US Constition. It also embedded the concept that these were limited, expiring monopolies. The first legislation to define them set them both at 14 + 14 years. Only in the revision of Copyright of 1909 was Copyright given a longer length that Patent. It was set at 28 + 28 years. I note this as until this point, Patent and Copyright were considered equals with equal protection under the law. The 1909 legislature vioded that point. I won't go into the further lengthenings, for brevity.
The sole purpose, as clearly stated in the US Constitution, was to encourage progress in the arts and industries. Not to support heirs, not to provide income to businesses in perpetuity, but to provide economic incentives for people to create - period. So the length of copyright should be set on the basis of whether or not it meets the purpose of causing works to be created, nothing else.
When you look upon the period of 1909-1976, a wide variety of arts were created, under the terms of 1909. So many items were created, that the the burden of proof is on the people who believe that longer copyrights actually caused more works to be created, after allowing for all other reason for creation have been take into account. (Still, Life + 50 or 70 years flat, or some other point may be shown to optimal. Evidence needs to be provided, not economic advantage of existing copyright holders.)
One final point. Once and item has been created, you cannot claim that later extensions of copyright would have had any effect on the items created on the existing terms. A writer or movie make in 1930, could not have know that their works's copyright would be extended multiple times <at the time these works were created>. Therefore they could have only based their long term value based on the laws as they wer at the time of creation.
Now, Hitch, if you disagree with any of the above. We can discuss the points. I've tried to "show my work" just like in a mathematical problem. If there is a flaw, let me know. But you seem to have a value base at odds with what I have described. Because of that, we'll never agree...(In my opinion (which may be totally wrong) you confuse the laws of Patent, Trademark, and Copyright with the laws of real property. That is not surprising, people in favor of more and more copyright love to call thes monopolies "Intellectual Property", so that people think the <are> property, with all the rules of property (particularly perpetuity) attached. That's not what the law is, nor has it ever been.)