I don't know that I fully agree with the parent's logic (despite the fact that I actually am a vegetarian), but I think the rationale to his argument is that humans are able to survive without meat (unlike cats, lions, or tigers), and we also have the ability to realize that we are able to avoid meat. Cats, bears, and tigers really don't have the mental faculties to know good or bad, or right and wrong, but we do (at least to some extent). If that's the case, shouldn't we avoid killing wherever possible?

Again, not sure I completely agree with the line of reasoning, but I at least see the point.

Non vegetarians everywhere demonstrably don't have the ability or "mental faculties" to see that eating meat is wrong, any more than lions and tigers and bears do.

It's like someone saying everyone has the ability to accept God or Jesus. No, we don't. And it's a touchy subject, because zealots tend to next infer that someone isn't fully human if they don't share fundamental beliefs or axioms.

Again, not saying that I fully agree, I'm just trying to explain the perspective.

Oh my.