That was a well written article too. I believe that the need to vent aggressive energy is because civilized culture has largely eliminated the need for the systems that produce that aggressive energy in day to day life. We evolved to fight off a tiger or bear or encroaching tribe on a regular basis but in modern culture, most go from chair to chair, to bed. Just like a pubescent teen will have wet dreams if they don't exercise their sexual organs frequently enough, modern humans have uncontrolled bouts of aggression from not exercising their adrenal and lymphatic systems. We're pretty simple animals once one gets rid of the parasitic culture we've fallen for.