Because, some argue, if all these sad young men could only get some, well, they wouldn't have the energy to kill anyone:
The theory, somewhat tongue-in-cheek, was advanced by the Independent's Howard Jacobsen, who declared,
If you're a man you don't fly before you're 30, is my proposal. And you don't go to university. You go out, get pissed, and have a lot of sex. That way we'll all sleep more safely in our beds.
It's been taken up in a more serious vein by the minds at Psychology Today, who concede that repressed sexuality is, indeed, a powerful force:
If our distorted relationship with human sexuality is the source of much of this frustration, confusion, and ignorance, societies with less conflicted views should confirm the causal connection. Developmental neuropsychologist James Prescott found that bodily pleasure and violence seem to have an either/or relationship-the presence of one inhibits development of the other. In 1975, Prescott published a paper in which he argued that "certain sensory experiences during the formative periods of development will create a neuropsychological predisposition for either violence-seeking or pleasure-seeking behaviors later in life." On the level of individual development, this finding seems obvious: adults who abuse children were almost always victims of childhood abuse themselves, and every junkyard owner knows that if you want a mean dog, beat the puppy.
Prescott applied this logic on a cross-cultural level. He performed a meta-analysis of previously gathered data on the amount of physical affection shown to infants (years of breastfeeding, percentage of time in direct physical contact with mother, being fondled and played with by other adults) and overall tolerance for adolescent sexual behavior. After comparing these data with levels of violence within and between societies, Prescott concluded that in all but one of the cultures for which these data were available (forty-eight of forty-nine), "deprivation of body pleasure throughout life-but particularly during the formative periods of infancy, childhood, and adolescence-is very closely related to the amount of warfare and interpersonal violence." Cultures that don't interfere in the physical bonding between mother and child or prohibit the expression of adolescent sexuality show far lower levels of violence-both between individuals and between societies.
Well, this is all very well, and I daresay there's an element of theoretical truth to it (although as any number of hapless "old ladies" of 60s radicals can tell you, regular sex is no guarantee against fanaticism. See Manson, Charles). But it's disingenuous to pretend that recruiting officers and crusaders haven't taken advantage of this for eons, employing essentially the same psychology. And what of the young ladies who are supposed to be queuing up to go home with these wild-eyed youths? We're all for public service - and who knows how many embryo plots we've all inadvertently foiled, as is? - but seeking out the loner who's prone to mind control is a bit much. Then, too, I'd take this inquiry a step further: might someone prone to such acts turn to another kind of violence, or rage, or control issue while in a relationship? Psychology Today: inquiring minds want to know!
Howard Jacobson: Twenty-two, Male And Introspective – Of Course He Should Have Been On A No-Fly List [Independent]
Sex Against War [Psychology Today]