I know what you mean, but for us it usually involves family members.
Before DS's diagnosis, certain family members blamed all of his difficulties on our "bad parenting". For example, they believed that DS could talk, but refused to becuase he was being malipulative and if we were stricter with him (ie withheld food) he would speak.
After, diagnosis, the pendulum seemed to swing in the other direction and these family members now think we expect too much from DS and "autistic kids can't do that." For example, if MIL stops by the house, I will prompt DS to greet her. MIL will say, "Oh no, he doesn't have to say hi to me. I don't mind. I know autistic kids don't do that." Or if DS is having trouble following a rule and I am trying to help DS understand and then a family member says, "Oh that's OK; I don't mind. I know its just the autism."
These situations drive me nuts. I will usually tell the person, "Well I do mind. We've been working very hard on [greeting people, following rules, or whatever]. DS needs more practice on this." Then I continue to help my son learn whatever it is I'm teaching him at that moment.
Gena
DS, age 11 and always amazing
“Autistics are the ultimate square pegs, and the problem with pounding a square peg into a round hole is not that the hammering is hard work. It's that you're destroying the peg." - Paul Collins, Not Even Wrong