Male aggression is partly hormonal. Testosterone is an anabolic steroid that’s been associated with aggressive behavior (roid rage) since long, long before athletes and bodybuilders began taking injections of it. Women have testosterone, too, at lower levels than men.
To the extent that aggression is associated with male reproductive dominance (common, I think, among apes in general) then genes that promote such behavior (in part by hormonal regulation in the adult; in part by programming fetal brain development; etc.) are selected for and survive over time—consistent with Darwinian evolution.
As for the nut cases in Idaho: Who knows what they were taking? What kind of cultural and environmental idiosyncrasies they shared? How shallow is their end of the gene pool? Many other factors…? Hormonal levels are probably correlated with behavior. not that all aggression is steroid-related. Whatever the cause, I gotta agree with @ragingloli that rape is “weak-minded.”