The physical limit is still irrelevant to the debate: the number of people who
want to use the lake could easily be far
less than the number of people who potentially
could use the lake. In this situation, the lake is artificially scarce according to the owner's property rights,
not because of any physical limitations.
The physical basis is just an incidental detail. The ethical basis is that individuals must use their minds to survive, meaning they must have ownership over the produce of their minds to survive, meaning they must have property rights. To say that somebody who creates a work, whether intellectual or otherwise, should not have control over its access/distribution, is to argue against property rights and indeed the right to survive.
As the previous poster argued, pirating/stealing my intellectual property amounts to removing my ability to profit from my creation/property, which amounts to direct (physical) harm to me, the copyright owner. True, it doesn't stop me using my creation, but that's hardly the point. What if I invent a perpetual motion machine, should just anyone be able to then tap into my non-scarce energy source without permission? Besides, saying property should be granted on the basis of physical scarcity says nothing about why it should be granted to a particular person - it's a poor criterion all round.