Nearly every culture that has ever existed has recognized that someone taking something from you by force is crime. Its a normative expectation for nearly 100% of all humans.
People like yourself, who don't see a value in others property (ie. think you are free to take it), are generally seen as very dangerous and inconsiderate people.
Yes, most cultures recognise some notion of property, few would agree with taking the clothes off someone's back. But the exact nature of these property systems is varied, and the idea that all things must necessarily have an owner, and anyone else using them is "taking them by force", is by no means universal.
Many cultures have some notion of public property, and indeed many of these public property rights were violated historically in order to establish the modern notion of private ownership.
Property Rights exist, at best, as part of a human narrative that we have some interest in designating a legal owner for a piece of dirt. Without humans, the dirt is not owned. With humans, we say we own the dirt (but there is no actual, objective ownership).
>People like yourself, who don't see a value in others property
I don't think GP made that point, rather that until Humans come along, no ownership, ie, public ownership, is the default. The land is owned by nobody until someone buys it.
This can be shown with an example; Mars. Who, at this current moment, owns mars? All the dirt on mars must, by your argument, be owned by someone.
Property rights are the first level of abstraction above the physical layer of "might is right". "Public" land is usually a higher level of abstraction, because it almost always still limits who is the public: even indigenous people usually mean "public" land as land of our tribe, not their tribe.
Property rights are still not an inherent part of nature.
If you break down the universe into component parts and sift through it all, you won't find any part that says "Property rights" and rather stuff like "Gravity" or "Particle Weak Interaction" or "Wave-Particle Duality".
If i'd own the river flowing by a big plant, would I care more about it's preservation than the polution-fee I could take from the company owner?
One last point: you call public land a legal-fiction - that's interesting, because I would call property rights a legal fiction, and "public ownership" the natural state of stuff (one could argue every legal concept is fiction, I'd tend to agree with that).