I'm not diagnosed as autistic or as a psychopath, but I'm really not a very emotional or social person. I take great pleasure in being alone, far from the madding crowd, and I find it much more difficult to be among other people, mandating the menagerie of masks necessary for me to get where I want to go in society w.r.t. my career etc. I say masks, because unlike many people I seem to meet, I do not have any enthusiasm for consumption, decadence and self-gratification.
I mean, I'm no buddhist or anarchist, I just prefer to perfect my craft over going out on the town or accumulating wealth I'll never use. I'm happy with cereal, I don't need some kind of smoked dolphin's nose on squid-ink dyed seventy-seed toast. I therefore have to act in a certain way, other than as myself, in order to be perceived to be relating to people I meet and work with.
In reality, you might call me a stoic, to use a loose definition of the term. I don't find it painful to act like someone I'm fundamentally not, indeed to act in an archetype I internally find rather absurd, but it is tiresome. It tires me greatly to be among other people, and I try to keep my relationships with others to a minimum. I have nothing to hide, I just prefer to spend time in solitary and uninterrupted recreation or study, refining skills and knowledge of topics I find interesting.
I'm not disagreeing with you, and I'm not saying that my individual existence is a significant indicator of anything contrary to your point, but my existence does at least indicate that some humans (since I find it difficult to believe I am alone) aren't as intensely social or pained by isolation as you say – and I dare say there's more than a little overlap between the set of asocial humans and the set of self-isolating hikikomori who prefer no company at all.
Though, in my experience on anonymous message boards over the past fifteen years online, hikikomori (or at least the western equivalent) seem to prefer the company of others like themselves whom they may encounter on said message boards. Or some certainly act like they prefer the imagined company of anime/video game characters to the company of other human beings, most of whom will never, ever come close to understanding them or what they're about.