Why should that difference matter, in particular when it comes to the principle I mentioned?

Because creative works are rather obviously fundamentally different from physical objects, in spite of a number of shared qualities.

Like physical objects, they can be distinguished one from another - the text of Moby Dick is notably different from the text of Waiting for Godot, for instance

More to the point, like physical objects, they're products of applied labor - the text of Moby Dick exists only because Herman Melville labored to bring it into existence.

However, they're notably different from physical objects insofar as they're quite simply NOT physical objects. The text of Moby Dick - the thing that Melville labored to create - really exists only conceptually. It's of course presented in a physical form - generally as a printed book - but that physical form is not really the thing under consideration, and more importantly, the thing to which copyright law applies (or in the case of Moby Dick, used to apply). The thing under consideration is more fundamental than that - the original composition.

And, bluntly, that distinction matters and has to be stipulated because selectively ignoring it in order to equivocate on the concept of rightful property is central to the NoIP position, as illustrated by your inaccurate comparison to a pen.

Nobody is trying to control the use of pens (or computers, as they were being compared to). The dispute is over the use of original compositions - compositions that are at least arguably, and certainly under the law, somebody else's property.

It’s not like AI is using works to create something new. Chatgpt is similar to if someone were to buy 10 copies of different books, put them into 1 book as a collection of stories, then mass produce and sell the “new” book. It’s the same thing but much more convoluted.

Edit: to reply to your main point, people who make things should absolutely be able to impose limitations on how they are used. That’s what copyright is. Someone else made a song, can you freely use that song in your movie since you listened to it once? Not without their permission. You wrote a book, can I buy a copy and then use it to make more copies and sell? Not without your permission.

I can see your argument it’s just your metaphor wasn’t very strong and I think it just made things a bit confusing

Google web integrity is very much different than what I’m proposing. “Nobody” was more in relation to regulating this.

I hold the opposite opinion in that creatives (I’d almost say individuals only, no companies) own all rights to their work and can impose any limitations they’d like on (edit: commercial) use. Current copyright law doesn’t extend quite that far though.

A creative work is not a reproduceable quantifiable product. No two are exactly alike until they’re mass produced.

Your analogy works more with a person rather than a pen, in that why is it ok when a person reads something and uses it as inspiration and not a computer? This comes back around to my argument about transformative works. An AI cannot add anything new, only guess based on historical knowledge. One of the best traits of the human race is our ability to be creative and bring completely new ideas.

Edit: added in a commercial use specifier after it was pointed out that the rules over individuals would be too restrictive.