The idea of the mass murderer being someone who kills, not in the heat of passion, but in a cold, calculating fashion tends to ignore the reality of hatred- the blood that never cools.
Some of the most destructive emotions we possess are the unreleased ones- that which remains unexpressed increases its power a thousand fold. In the cult of masculinity, the inability to show the true nature of one's feeling exacts a toll, sometimes a gross and terrible one.
Anger becomes , to quote Pickard, like old leather; so comfortable one can not remember feeling any other way. More devastating, however, is the belief that the emotional pain of the present experience will never abate. This fire of hate, fear and pain congeals into a rage that burns unceasingly; and its flame consumes the portions of humanity that would prevent acts of atrocity.
With blood at a perpetual boil, cooler heads can't prevail; once the liquid evaporates, the scorched flesh begins.