This has been bugging me for a while. I'm probably not going to say anything new, but I think a thread discussing the matter here would be nice. If we want to have perfect ethics, why should we apply the NAP only to humans? Why would one justify aggression against other animals? But in fact, why just animals? Why not also apply it to every other living being? Perhaps to non-living things as well: maybe it's atoms that have the property right, or maybe it's subatomic particles that do.
Also, all this poses a big problem. If it's true that it's not justified to violate their property right (if they have it), this makes it impossible for us to do anything without violating ethics, since merely developing the land or even just existing causes the death of some other beings or things, and it would make us aggressors by default.
This might all sound quite extreme, but I wanted to push the argument to the absolute limit.