Maybe my definition of “person” isn’t quite standard, but I did have otherkin in mind; to me, a person doesn’t have to be human to be a person. My cat is a feline person, or near enough, Commander Data is a (fictional!) person, etc. Practically zero people want to give up their personhood, at least in everyday life, as it’s extremely disadvantageous and unpleasant. It’s in this sense that saying “an autistic person” rather than “an autistic” is much better: however you identify, you’re a person, an individual with rights and worthy of respect, and not a thing that one would only bother identifying with an adjective. A vital part of being a person is having more than one aspect. A lot of racial epithets are offensive for the same reason.