But why are they violent? Latent (homo)sexual energy, apparently. I can't remember the exact quote, but that's ol frank for ya.

Edit: "The all-male army has a tendency toward homosexual activities" Something about the "breeding males" (older men) sending younger "non-breeding males" to war as a "screening function". So then you have all these young guys who have some options with what to do with their pent up energy when denied an "external enemy" - either be gay (apparently) or, since that is discouraged, they "sublimate" those energies raping and pillaging - hence being dangerous.