For knowledge to have power in this context, it must be you-specific knowledge. You should not care what 66% of people do in this context. You should care that you have specific and identified strengths and weaknesses. For example, testing might show that you can read subtle emotion in voices, but you can't pick signals up from faces alone. That's an example of knowledge you can act on to make your life better. The fact is, you ARE that way. It's not new, and you're not getting worse. You are already living your life in context. Understanding can only help.
Next, I'd like to address another important point . . . the risk of a wrong diagnosis. People say, What if I get an Asperger diagnosis when I really have ADD? Can't that be harmful?
That actually goes back to my comments on the dangers of labels. To me, the label does not matter. What matters are the specific insights into your own behaviors and identification of your personal strengths and weaknesses. There is no hazard to learning those things. I agree that diagnostic errors can be harmful, but that too is another subject.
Don't focus on the label. Focus on the behavioral insights. Ask yourself, does the result make sense? If it does, you are the way to improvement. If it doesn't make sense, question the tester. Perhaps the results don't mean what he thought. In the end, it is the specific behavioral insights that allow you to make a better life, not a broad brush label.
People are not labels. Our personalities are made of countless eccentricities and aberrations, and it's those I seek to understand. The power is in the details. There is no power in a broad brush label.
Finally, there is another danger of diagnosis. That is with your medical record. What if you receive an autism diagnosis and it's entered into your "official" record because you had the testing done by a professional who's paid by a health insurer? It's possible that you could be rated unfavorably for insurance, or even denied insurance later in life.
What to do about that? The only answer I know is to pay for testing on your own, and make your own decision where the results are released. I would have some concerns about having any diagnostic information in my medical record because the evidence indicates insurers sometimes try and use those records against us for their own advantage.
So the issue of "downsides to the diagnosis" is not as clear-cut as I originally portrayed. I apologize to those who felt my original post was misleading or incomplete.
For more of John's insights check out his blog Look Me in The Eye