high test=risk seeking, adventure seeking, status seeking. army gives them further status while allowing them to partake in high risk behavior. the higher the risk, the greater the dopamine rush when they successfully kill the shit out of the enemy. it's the same reason they like football and other contact sports. you are risking bodily injury, but if you win, it not only reinforces dopamine pathways(wich reinforces the behavior), but it raises your testosterone even higher.
a very interesting facet of environmental effect on chad development.