Unfortunately it comes down to the stigma many have thanks in part to crap portrayal of Autistics on the news and tv/movies. They've seen the rainman's and I am Sam's and just assume that is everyone with Autism. That it is a spectrum, many people are simply ignorant of that fact.
Those folks honestly aren't worth your time, and aren't worth getting upset over. Yes they are frustrating, but at the same point with 8 billion people on this planet, some of them are just going to be not nice people in their views. And I am not going to say they are being mean on purpose, well some are but most aren't. "Never attribute to malice what can easily be explained by ignorance".
If they seem receptive to learning more then it's worth having a dialogue with them. A lot won't be receptive, especially the crowd that thinks Autism is something to be "fixed". Best just to ignore them and move on. Be like Bob. Marley and realize that you "Can't please all the people all the time".
Stigma is a tough battle. I am also an addict, alcoholic to be precise. And while I've now been sober for years there are still that type of person that the moment they find out just view me as social pariah. It really bothered me in the beginning, now though it's a screening tool I take pride in. I know my worth, I don't need their approval. So when I meet someone that is going to look down on me and just run with the stigma, I move on as they are not worth my time.