There is a word that hasn't come up in this discussion, and that's Asperger's. I know some people with Asperger's who are very oppositional and some who are not. Given that ADHD is sometimes considered the tail end of he Autism-Asperger's spectrum (not always, this is new and controversial), I think it is reasonable. As top commenter bjhoops says: "it is probably much more common that some kinds of mentally ill individuals happen to be anti-authoritarian."
And I don't really agree with it either, but Einstein has often been co-opted by Asperger's support groups as one of their own.
From my admittedly limited reading on autism, Asperger's, and other behavioral diagnoses, they are not mental illnesses but rather alternate "wirings" of the brain. People on this spectrum can (to varying degrees) learn to deal with the "neuro-typical" world around them, but they can't change their brains. And these are not one-dimensional conditions: people on the spectrum have any number of different wiring, from social handicaps to language problems, hypersensitivity to touch or noise, face recogniition, etc.
I suspect that anti-authoritarianism is one of these dimensions. It can exist on it's own in an otherwise "neuro-typical" person, but it often gets added to other deficiencies on the Autism-Asperger's spectrum.
I am not saying that blind adherence to authority is "typical," but I think there is often a recognition of parental and social authority that is mostly normal which is what the anti-authoritarian lacks.