Perhaps first and foremost, it is just entering the scene. It hasn't had time to obtain mainstream acceptance, and admittedly it took other disabilities decades to achieve any kind of serious acceptance. The deaf movement for example started around the turn of the 20th century, but didn't really achieve much until ADA and even more recently "Deaf President Now".
Next, it is very easy to deny, especially with higher functioning autistics. While most people have no problem labeling a nonverbal child who is still in diapers as being autistic, when you can look and appear normal, for any amount of time, a lot of people (on both sides of the political spectrum) deny you have autism. This makes acceptance harder to get as you are being seen as just being *insert adjective here* and not truly disabled.
Lastly, because it does have that lower functioning side, and that is still what most think of when someone mentions autism, it is hard to say that a person with that exact same disability (especially as the term Asperger's is going byebye as of DSM-V) can be a teacher. What amazes me about this is how much this train of thought effects those hired to work with autistics.
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