I was not clear enough, apologies. Naturalness is not the reason that things should be owned in common. Rather, the reason that land ought to belong equally to all is because unchecked exclusive ownership reduces the freedom of non-landowners. It is thus incompatible with a classical liberal view that celebrates individual freedom.

If I build a fence and claim everything inside of it, you might find that reasonable. If I build a fence and then successfully claim everything outside of it, then I have in effect made everyone else prisoners inside of the fence. And if a subset of humanity claims the entire Earth, then the rest become like trespassers to be dealt with however the landowners saw fit. The rents they demand could be unlimited, since everyone requires access to land.

Every parcel claimed reduces the amount of freedom of everyone else, and eventually all land becomes claimed and rents begin rising in tandem with the progress of civilization, putting people into a position of serfdom. And that is why no amount of technological progress will ever eliminate poverty.