This is the most fascinating part of mental illness. And it's a bittersweet thought that as horrible as mental illness is, it might be what allows us to really understand the human mind.

However, making evolutionary arguments for psychological traits is tricky business and while I'm not a professional evolutionary psychologist myself, I think the explanation you gave violates a fundamental principle of evolutionary arguments.

Imagine gene A confers a fitness advantage because it allows a person to better cope with a selection pressure X, and gene B confers an additional fitness advantage against X, but only if gene A is present, and does nothing otherwise. In this (common) case, gene B will not be selected for unless gene A is already universal in the population. Following the same rules, imagine we then get gene C which is dependent on B, then a variant of gene A called A* which is dependent on B and C, and so on. Eventually, if even one gene is removed (either by sexual reproduction with someone who doesn't have it or by mutation), the whole tower falls down and the entire piece of complex biological machinery is broken.

Basically, there's no way for selection pressure X on a significant chunk but not all of the population to produce a piece of complex machinery (read: involving 2+ interdependent genes) in the first place, and it would be broken beyond all repair in all offspring who didn't have both parents with the full genetic instructions. So the idea that "many humans were abused, enslaved, etc." only works if the selection pressure was on everyone and the adaptation is universal in the human population, unless it's attributed to a single mutation.

The rarity of this condition isn't consistent with it being a feature. Seems like a bug to me.

Hope this was helpful!