"another species using the same resources is an enemy" was meant to apply only to non-sentient species. Almost all such species are basically built with hard-wired instructions to convert as much of the planet as they can into copies of themselves. They are restricted only by the physical limits on them, and by other species killing them off. They will destroy competitors, eat everything they can eat, and ignore most things that don't fit into their particular niche or affect their survival. Now and then you will find a nice symbiotic thing going, but only where both sides are getting something out of the deal, and never with a species that directly competes in that niche.

You will never see a predator in nature pull back from their prey wondering "gee, maybe I'm eating too many of these guys?"

Obviously, a sentient species has the advantage of being able to predict and plan, and doesn't always have to wait for nature to slap it down the hard way. Humans have a better way of doing things, but that hard-wiring is still under there somewhere, and it causes a lot of trouble when it isn't suppressed. Xenophobia didn't just pop out of Pandora's Box. We evolved it the hard way.

Just as an aside, I also laughed when I said to myself "And if Tom applied that philosophy to politics he'd be a Liberal!". But I digress...

Actually, the metaphor for liberal philosophy would be a lion trying to learn how to fly off a cliff by watching a swallow, or breath underwater by watching a fish. ;)