There should simply be perpetual copyright. Intellectual property is not inferior to physical property.
Okay, so, this is... unwise. First of all, "intellectual property" is a fiction permitted only by the human constructs of copyright, patent, and trademark law, whereas physical property is permitted by physical limitations of the universe - there's an object, I have it, you don't, you want it, we can barter, and then you'll have it and I won't.
I couldn't disagree more. That's like saying freedom of speech is a legal fiction. The law doesn't create (or destroy) rights, it only acknowledges (or denies) them. That's as true for creator's rights as with anything else.
Perpetual. Are you seriously suggesting that a licensing fee needs to be paid to the descendants of Thomas Paine, for example, for distributing the text of "Common Sense"? Or that companies should still be licensing a patent in order to make, for instance, basic cookware? You would grind civilization down to a slow crawl to benefit IP holders, most of whom aren't even the people who came up with the idea in the first place.
Well, I hardly think you have to worry about any changes in the law being retroactive 250 years.

Or at all. You can't change the past, you can only cultivate the future.
OTOH, couldn't we say generations of heirs should come up with their own thing, rather than kicking back and cashing in on something great-great-great-granddad did?
What about a house that's been in the family for a few generations? Should the government kick them out and tell them to get a job and buy their own house?
There should simply be perpetual copyright. Intellectual property is not inferior to physical property.
It's hard to weigh superior/inferior because they are inherently different. There is no physical limitation on the IP; anyone could duplicate it a million times and it would not deprive the creator of the ability to use it.
No, but it's depriving them, even theoretically, of income and it's taking away their right to control what they created. Bill Watterston has chosen not to take advantage of licensing opportunities for
Calvin & Hobbes, based on his own personal principles. If someone makes money with C&H products without his permission, they are both stealing from him and misusing his property. Scott Adams, on the other hand, will do anything to make a buck from
Dilbert, so if someone makes money with
Dilbert products without his permission, they are compromising his income and stealing his property.
Copyright (and patent) laws are intended to benefit society, not individuals. The mechanism used to encourage people to create works that are useful to the public is to secure for them the monetary benefit of the work for a period, but that is a byproduct, not the goal.
From each according to their ability, to each according to their need?
With the news covering things like extending patent on old medicines to jack up the price, tech patent trolls, lawsuits over the "Happy Birthday" song, etc. I would have thought that the benefits to society of the public domain would be pretty obvious by now.
There's always a benefit to free stuff (and always people trying to sue for money they don't deserve), but that doesn't mean it's okay to steal from someone.