I agree. I remember telling a friend of mine when I was diagnosed with autism spectrum disorder and I told her “I have autism” she responded with “no, you don’t have autism, you’re autistic.” Which really offended me.
It’s my condition and I have my feelings about it, don’t police what I call myself. Yes there are many autistics who refer to themselves that way, but I don’t quite identify the same way. I think of my autism as something I have, not something I am, and it’s not ableist. My whole life people have seen things that were actually my autism, but weren’t me, as being me. My autistic traits were written off as personality, quirks, eccentricities, stubbornness, or my attitude. They were not, I had no control over these things and I don’t do them to be cute, which is what people thought. I don’t like my sensory issues and how they hell put me through, I don’t see them as a part of me. I feel I more than my autism and I’m a person first, and autism is a thing I have. I don’t think I’m ableist for the way I feel about my own condition yet many autistics disagree and are happy to lecture me on how I should feel or think they speak for all of us. They don’t. They can refer to themselves as the please, and I can refer to myself as I please.