This only works as a reductio if you consider people and animals to have the same moral worth, and relate to them in the same way. If that kind of view is a necessary foundation for vegetarianism, then vegetarianism just becomes even more absurd. The overwhelming majority of vegetarians don’t believe anything of the sort.
If eating animals has positive value because it contributes “to the continuation of these species” as you’re claiming and humans have greater value than other animals, then a logical conclusion is that eating humans has even greater value than eating other animals because you’re maximizing the continuation of the most important species. It does not at all require equivalent moral worth.
This only works as a reductio if you consider people and animals to have the same moral worth, and relate to them in the same way. If that kind of view is a necessary foundation for vegetarianism, then vegetarianism just becomes even more absurd. The overwhelming majority of vegetarians don’t believe anything of the sort.
If eating animals has positive value because it contributes “to the continuation of these species” as you’re claiming and humans have greater value than other animals, then a logical conclusion is that eating humans has even greater value than eating other animals because you’re maximizing the continuation of the most important species. It does not at all require equivalent moral worth.
EDIT—reworded for clarity
But it does require relating to them in the same way, so re-read and try again.