Without denying our desperate need to--for the sake of our own survival--address the inextricably-linked issues of unsustainable human population growth, and criminally inequitable misappropriation of natural resources, it's nonetheless necessary to point out that environmental degradation due to human-engendered invasive species is an ongoing and deadly threat not only to other native species, but to ourselves.  And cats are among the worst species in that regard.

Having said that, your argument is merely an (unusually carefully-stated) example of the logical fallacy of deflection, and no more sensible than arguing that we should ignore cancer because heart disease kills far more people.  Or that those Texas klansmen who dragged a black gentleman behind their pickup until his HEAD popped off in 2008 shouldn't have been imprisoned because the Da'esh ("ISIS") behead far more people.

This is in fact one of the cat-nutters' most frequently resorted-to fallacies.