I'd like to pick up on one interesting point in the first post. I also suspect a lot of ASPD gets misdiagnosed as ASD. They are nothing like each other, except in terms of outward appearance.
I may stir up some controversy, but my way of having autism does not shut down my emotions. I thought I was unemotional, because of unwillingness to completely melt down if possible. That led to some notable events where I displayed less emotion than others, and a sense of being emotionless. Ha! I now accept my empathic and individual feelings, and gain strength from them. Narcissists cannot achieve that, by definition. They are an emotional hole.
Also, there's a difference between not knowing about social cues, and not caring. People with autism may get so frustrated and angry that they give up, or want to give up, on caring about people, but it only comes naturally to genuine sociopaths. That's a huge difference in reality, but it presents the same to psychologists in a lot of cases.
So, put yourself in the place of a shrink of whatever sort. You can choose a plausible diagnosis of antisocial personality disorder of some sort, which is untreatable, or you can choose a somewhat less plausible diagnosis of autism spectrum disorder, which is super-manageable, and barely even a disorder in many cases. There's no incentive to diagnose ASPD, except for a specialist in that area, maybe.
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"I find that the best way [to increase self-confidence] is to lie to yourself about who you are, what you've done, and where you're going." - Richard Ayoade