One of the more defining elements of autism is a disregard for conventional values and norms. At its root, this is not ideological, although ideological nonconformity often develops as a consequence. When this inability to connect with others is severe enough, autistic children have trouble even learning to speak. This is because they aren't mirroring caregivers. They don't learn the basics the way others instinctively learn.
Even for the most brilliant of us, this can be a profound learning disability. It creates a cascade of consequences as the autistic individual progresses through life, learning how to cope, learning how to act normal, but never actually being normal, and coping never becomes easy. Neurotypical behaviors are called mainstream precisely because that's where the flow is the strongest and most common. It's not a choice to be outside the mainstream, so much as the absence of learned behavior that typically draws people into going with the flow.
Autism is a spectrum, not because it varies in severity, but because without conformist instincts to guide us, we learn to get by in our own ways. Every individual's life experiences are different. These experiences then guide development in a wide range of different ways. We don't follow any sort of standard autistic path, but are forced to forge our own paths, and we go in all different directions.
This often makes it very difficult to relate to others and form healthy relationships. Even other autistic people can be so different from one another as to make connection feel impossible between them, never mind connection with neurotypicals. When people don't share similar values, and have lived our whole lives accordingly, it can result in a devaluation that goes both ways.
A basic example might be materialism. This is simplistic and people are more complicated, but to illustrate the point, someone who doesn't value wealth or owning stuff will probably go through life with very little. Work is not only more difficult for such an individual, but their incentive to work is also greatly diminished. The importance they place on this basic measure of social value might not only be diminished, but negative- it's not something we're going to value in others, either.
Another example might be vanity. This one applies less to myself, but I know it's also common. A person who is indifferent to appearances will not put effort into their own appearance, nor value anyone else's. They might go through life being judged for how they look while judging others for caring about something perceived to be meaningless.
Autism is strongly correlated with social deficits, such as difficulty making small talk and other related conventions. So, even our personalities can be seen as lacking, while we might find those same social behaviors to be irritating, and worse than worthless. We may try to mask these differences, because this whole dynamic can make life so alienating and difficult, while on a deeper level, hating the prospect of being more like everyone else.
When such differences are framed as disability, that is a devaluation. This is why there's often controversy around framing autism as a disability. We do not bring to the table what others are looking for, and that they place importance on things we deem worthless can make them seem like idiots. We go through our lives struggling to find our way in a society clearly built by idiots. If we fail to connect with others who share our values, it can be a very lonely journey.