We can respond to threats with fight. Or flight.
A man should be capable of extreme violence, as needed. But he should avoid gratuitously or randomly engaging in violence. Or refrain from engaging in violence when this presents significantly higher risk than acting on the other instinctive response he has evolved for: Flight. This self-control, and risk assessment capabilities under stress, are what separates men and warriors from psychopaths and hysterical vaginas. A man should essentially always keep it under control. A similar behavior is also prevalent in nature, with wolves or bears with cubs or pups avoiding unnecessary risk when faced with a threat so the offsprings do not end up in a more threatening situation.
I have been exposed to my share of psychopaths so far in my life, military and otherwise: ISIS, Ukrainians, North Koreans, Chinese, and the average Canadian. Including, for the latter, earlier today.