Playing devils advocate for commies:
Isn’t ownership over physical goods just as much an unenforceable idea? Because you found it first you now have some claim to an abstract territory or item?
Except in terms of denying society opportunity, denying a physical good is worse. Because it IS scarce, you are denying vital necessity to others based on nothing but an idea if ownership or use of force.
It's called "homesteading" in some circles. The first person to claim and use a resource, which could be land or something like radio bands, gets ownership.
Though whenever you come up with a new society that enforces property rights in the exact way you prefer, you also have to deal with all the people who already owned stuff, in the earlier system. The typical way this is handled is they get to keep their stuff, but no special privileges. This is pragmatic, rather than fair. A bunch of nobles whose great to the Nth grandads were really good at killing people and taking their stuff don't deserve more than the peasants they've subjugated for generations. But the alternative is social chaos and disruption, potentially leading to the overthrow of everything, like the French Revolution. The reason this is considered an acceptable compromise is the allocation of resources throughout society isn't static. It changes, and as long as the government isn't handing out special privileges like a cronyist fairy, in a couple generations resources will shift to those are best able to use them for the benefit of others.
And you're missing the point of scarcity. It's because physical resources are scarce that someone must own them all. Because if everyone owns something, you get the tragedy of the commons. The resource in question will either be overexploited or trashed, because there's no incentive to take the the extra effort to clean up or maintain or ensure something is continually productive when you only have a tiny share of it. Conversely, a person who owns it and thus has full claim to all the future benefits of it, has every incentive to ensure the soil isn't depleted or the huge trash piles are removed. Since it's better cared for it, it's more productive. And when all of those resources are connected in a free market economy, the resources will distributed to theri more productive use. So ownership ensures all the resources in the world are put to their best uses. That's the whole point of property.
Conversely, with ideas, there's no such restriction. Ideas don't need maintenance, and aren't depleted by overuse.