There's a lot on the web about various developmental and personality issues, including Asperger's and especially narcissistic personality disorder, with the latter being relevant. It sounds believable that one could develop delusions of grandeur where one believes he is acting like a god punishing and eliminating the wicked or the unworthy (this makes Rodger sound like Hitler to me). But if sex is evil, as the "manifesto" seems to imply, why does he feel entitled to it anyway. All "logic" breaks down there. Only a couple of men who have performed rampages have gotten "manifestos" published (the Unabomber); in the VA Tech case, a screed document was sent to NBC News but never made public.
On "Days of our Lives" (July 1), the character Daniel Jonas says to Brady "A sociopath is someone who has no feelings beyond his or her own urges". He's talking about Theresa. That sounds a bit like Elliot.
Susan L. Ruth, on Communities Digital News, has a perspective that talks about Schizoid Personality Disorder (itself harmless) in conjunction with "Borderline Personality Disorder" here.
It's also useful to compare Asperger's Syndome (a form of "mild" autism") with schizoid personality disroder (which is not), here.
Not many people want to mention this, but it seems likely that Elliot's perception of himself as mixed-race was also significant. That's not always the case -- it's true of the president, but in some situations it still is.