> What we're talking about here is a concept of legal ownership,
Nope.
> The alternative to that, historically, is usually not everything being communal, but rather power resting with those wealthy or otherwise powerful enough to enforce their claims of ownership independently rather than relying on the state.
That's kindof a self-referential definition, isn't it? The power to defend property was with those who had the power and the property ... yeah, obviously?
All of that is rooted in social norms. What does it mean to have wealth? What does it mean to have power? Sure, if you have a gun, I guess you could say that that gives you power somewhat independent from social norms. But the moment you try to get someone else to use their gun to defend your property, they could potentially just ignore your request, and that would be the end of your power, and consequently of your property/of your wealth.
Power and property are granted by society, not an intrinsic property of the powerful or wealthy person. And that applies even to "communal property".
> This one is easily argued on "veil of ignorance" grounds, I think.
As can the equal say of everyone in deciding on copyright rules? That was kindof my whole point: The weight of your opinion should not depend on the position that you end up in in society, be it a slave, a slave master, a "content creator", or a "content consumer".
> I don't think we're really talking about just being able to do these things under your own control, though for the record I challenge your claim about exemptions; I know of no jurisdiction where it is legal to copy content even for personal use when you've explicitly agreed not to as part of something like a PPV deal.
Really, I am not sure how things map to modern technology and the business models/contracts it enables, and in any case, it's usually not just a blanket permission to make as many copies as you like, but there are quite a few options of what is in US law usually called "fair use":
https://en.wikipedia.org/wiki/Fair_use
Those exceptions usually exist for very good reasons, and are part of the rules that society decided to be a fair deal. Now, if modern devices/software intentionally don't implement the functionality that would enable people to make use of those exceptions (in addition to possibly illegal activity), that de facto takes away people's rights, which is why it's morally questionable: The software does not distinguish between a user exercising their right to, say, pull an excerpt from some video to create a political commentary on it, and another user illegally making a copy of a movie purely for entertainment purposes, it just enforces the wishes of the creator/platform.
> I think it's quite clear that relying on voluntary donations alone does not.
I am actually not that convinced of that, but well, sure, some things might be difficult to finance on that basis.
> What we're really talking about is how much weight or influence any given person's opinions should have on anything or anyone else, and I think the view that those doing the work from which many benefit should have more influence than those who are not contributing anything of value is at least a rational position to take.
I think you might have inadvertently changed the topic: TheSpiceIsLife's comment referred to how much weight their opinion should have in determining the rules of society (in this regard). Your argument doesn't really make much sense in that context, as valuation is subjective and exactly the subject of political discourse, and it doesn't make sense to say that the creator of some thing should be given special privileges because they themselves value their work highly--and if you base the decision instead on how the rest of society values their work, you have just found a confusing way to say that everyone should get equal say in what the rules ought to be.
Your argument makes sense as a principle for how the rules that are to be determined should distribute power, not so much for who gets the power to decide the rules in the first place.