Three hypothesis which may not be mutually exclusive:
1) Some people disagree (with you) about whether or not some animals are persons.
2) Some people disagree (with you) about whether or not being a person is a necessary condition for moral consideration - here you've stipulated 'people' as 'things subject to moral concern', but that word may too connotative laden for this to be effective.
3) Some people disagree (with you) about 'person'/'being worthy of moral consideration' being a binary category.
r/Fitness does a weekly "Moronic Monday", a judgment-free thread where people can ask questions that they would ordinarily feel embarrassed for not knowing the answer to. I thought this seemed like a useful thing to have here - after all, the concepts discussed on LessWrong are probably at least a little harder to grasp than those of weightlifting. Plus, I have a few stupid questions of my own, so it doesn't seem unreasonable that other people might as well.