Suppose that within a few generations a large percentage(70%-90%) of humans were born with at least mild autism.
Autism would only become the norm in the human population if it is an inherited condition and it confered a selective advantage.
At what point would this new population start to breakdown due to the inherent social challenges posed by this condition?
If autism confered a selective advantage, it could change the social status of the human population. The new "evolved" population would be different from the original but it would not breakdown, it would just be different.
With this condition being in the minority, we are able to mitigate the effects on society through additional educational and developmental work as well as some pharmacol treatments of debatable success.
The fact that autism is the minority suggests it does not confer an advantage.
In a majority situation would they be of any help to the species as a whole?
Evolution does not work with the objective of helping the species as a whole. In fact, the species as a whole would be better off without evolution. Evolution means species change over time becoming other species and often the ancestor species becomes extict in the process. It is the new and "evolved" species that receives the benefits of evolution, not the old one.
If autist individuals became the norm, they would benefit, not the "normal" individuals.
Would the primary signs of the condition, the diminished social ability, and communication challenges out strip our ability to adapt to the condition as a norm?
Depends on what is more beneficial, autism or our social ability. If autism were more beneficial it would prevail and a new form of human society would emerge. Maybe humans would cease being a social animal. Judging by what actually is the norm in the human population, it seems our social ability is a more advantageous strategy.
If the success of modern humans is primarily attributed to social cooperation, how much change in social ability could be tolerated over the course of a few generations? Is it even conceivable that an immune response to pathogens could cause a collapse of not only civilizations, but also in our case, survivability of the species as a whole?
2 possible scenarios:
a) social skills are the most advantageous adaptation limiting the spread of autism inducing immune response.
b)autism inducing immune response is the most advantageous adaptation causing the collapse of human social skills, which in turn leads Homo sapiens to evolve into Homo not-sapiens-anymore.