I could breed a human baby for meat, and it, too, would exist to fulfill its purpose by dying. There are two major differences:
1) You probably place value on the baby's life and its ability to suffer, whereas that seems not to be the case for farm animals.
2) The government also places value on the baby's life, and disagrees with my assessment that its purpose for existing is to feed me. This at least serves to prove that different observers can disagree about a being's purpose, and opens the door to the fact that the animals, at least, do not agree with you about what their purpose is. (They won't say so, but the government has nothing to declare about the baby's purpose either, only that I may not kill it.)
The argument is based on the idea that farm animals exist to be useful to us, and since that isn't objectively true, I don't see that the argument reveals any objective truth.
1) You probably place value on the baby's life and its ability to suffer, whereas that seems not to be the case for farm animals.
2) The government also places value on the baby's life, and disagrees with my assessment that its purpose for existing is to feed me. This at least serves to prove that different observers can disagree about a being's purpose, and opens the door to the fact that the animals, at least, do not agree with you about what their purpose is. (They won't say so, but the government has nothing to declare about the baby's purpose either, only that I may not kill it.)
The argument is based on the idea that farm animals exist to be useful to us, and since that isn't objectively true, I don't see that the argument reveals any objective truth.