The apparent lack of empathy does not equal sociopath. I'm on the autism spectrum. I seem to lack empathy lots of times. Often because I don't get the situation, especially body language. Other situations, I'm overdoing it with empathy... but that's not usually in gaming situations.
A lot of players I met, my groups or game meets/conventions, fall on the autism spectrum, them knowing it or not. Your "dark loner" type may be one of them. The guy who doesn't bath often enough, probably for sensory reasons, may be one of them. The couch potato with no other friends probably, too. You wouldn't know, as most people, if they are even aware, don't broadcast the fact.
When I started playing, almost all in the group were intellectual loners, outcasts not fitting into other groups, using RPGs as a mental exercise and/or as an escape from their often not too great lives. As the hobby spread, we started getting angsty people with the need to kill something, however fictional, well adjusted normal people who just wanted to live their own movie, book freaks wanting to delve into their own imagination and so on and so on... a really great variety of people. Getting groups fitting together could be difficult at all times.
The older we got and the more generations were spread out in the groups, the more normal the selection of people became. Now the groups include people barely able to catch up at school (who tend to get better due to RPGing, especially with maths and language), housewives, out of work people, miners, doctors, lawyers, school teachers, factory workers, cubicle workers, salesmen, scientists...
Still lots of intellect present, but as many average or even admittedly below average IQ people. We used to have a mentally disabled girl back in the 90s who still managed to play well enough so you hardly noticed. Still many players on the autism/AD(H)D spectrum, but as many who are, as we say here, Otto Normaluser. From extensive hobbyists to 4 times a year weekend players. From maths geniuses to people who can barely figure out their damage values without help (me, actually - discalculia

). From people who write for a living to those who can barely read their CS. As long as you have players willing to help others with their difficulties, it works out.
So maybe RPGs were once a super geek high IQ phenomenon. Not any more. The amount of loners vs social people is balanced out as well, with actually more people leaning towards being social.
It all depends on how you look for players, though, as I found there are people who would love to play but are intimidated by this outdated image of intellectual superiority, fearing to enter a group of wannabe Einsteins with their normal IQ. If you make it clear that everyone is welcome and don't tolerate those looking down on players unable to get the maths quick or try to tell others how to play, you may get the kid next door who can't get above C grades. And it may help him with real life skills, too.
