Please don’t take this personally but why do most people treat autistic adults like children?

I worked with Autistic adults for a couple years. It was some time ago. NO ONE understood Autism and we dealt with them incorrectly until there was more information. I have scars on my arms because they were so angry and frustrated and misunderstood The people I worked with were thrown into Institutions,they threw anyone in there, Downs syndrome, Epileptics, depressed people. None of those folks should have been there! Autism is just now coming into the light,still not enough information or understanding though. I know it's frustrating to be misunderstood but, when someone treats you like a child, instead of getting angry and expecting everyone to understand Autism, it is your DUTY to teach them otherwise...a teachable moment. Educate them. That would be a very mature thing to show them. I know what I'm talking about. I have a physical disability and live in a wheelchair. Sometimes when I am at a restaurant with friends the waitperson will ask one of my friends what I would like to eat, instead of asking me, because since I was in a chair I must be braindead. I enjoyed shocking them by pointing out what they did with a sense of humor. That was a lesson for them. Lower your expectations of people, have a sense of humor and teach them. I don't believe people who treat you that way are being mean...they don't understand.