Persuasive arguments should focus on what's good for the world today.
I will however say that I think my comment was not just an appeal to authority. Again, I think the fact that using public domain works was critical to Disney's early success is a fairly important data point, especially considering some of those works would not have allowed to be used with the current lifespans (e.g. Pinocchio's copyright would have lasted until 1960, 20 years after the film premiered).
But again, the most important thing I want taken away from this is that we the "consumers" of the content should not consider ourselves bystanders, but understand that we do have an active stake here as well. You're first sentence is perhaps more important than you realize, making up the rules wasn't something one-off incidental property of being first to the table, we could choose to make up the rules too, so we should act like it, as opposed to trying to "deduce" the ownership of a sentence. This is unique, we don't have that ability with physical property. We can't simply declare that everyone gets Ferrari tomorrow and then have them magically appear in everyone's garage. But we could declare that everyone can have the rights to Superman tomorrow, and they would "magically just have them".
There's no real baseline here. We should just weigh the pros and cons. The fashion industry operates more or less copyright-free. The infrastructure to enforce copyright has real costs. Not to mention there is all the collateral damage from the abuse of copyright takedowns this system brings along with it. And any sort of appeal to authorship is also highly suspicious given that authors rarely end up owning these rights. Every time one of these Marvel movies comes out there's a mini outcry when people see the guy whose comic the movie is based on is just some dude who gets nothing from the making of the movie. On the flip side we take for granted that every public domain character was of course at one point created. Robin Hood, Zorro, Dracula, Sherlock Holmes. Are we unhappy with the diversity of adaptations we've gotten from these? Would it be that Earth shattering if Harry Potter joined that list? As things stand right now no one on this website will likely ever get to legally publish "their take Harry Potter". The clock doesn't start ticking until after JK Rowling dies. It would have entered the public domain 2011 under the original rules. In case you're curious, her net worth in 2011 was $500M, if you want to factor that into whether you think that would have been "fair" (and its not like she stops making money at that point, its just other people start to be able to do stuff with the first book). I think it is worthwhile to imagine a different approach to this.