Aggression can be categorized along the lines of the epic Spaghetti Western film directed by Sergio Leone The Good, The Bad and The Ugly. Studies have shown that the appetite for aggression is a fundamental part of human nature, which can be evoked in all almost all men and some women.
In a review article from the journal Neuroforum, the authors discuss the inherent lust for appetitive violence that has been shown to be a fundamental part of human nature. The review highlights the different patterns of aggressive behaviour and the genetics and psychology of appetitive aggressive behaviour – the positive feelings associated with the execution of violent behavior.
The authors point out that a latent passion for fighting and dominance can probably be evoked in almost all men and in some women. The snowballing outcome of groups, tribes or communities that enact this aggression is war and destruction, to the point of trying to extinguish entire ethnic groups. Like the title of the famous Spaghetti Western, the three types of aggression can be categorized as so:
The Good means fighting to counter threat for your life or your loved ones. This aggression is a reactive defense, morally justifiable and marked by arousal with a negative valence. It subsides when the fight is successful. As such, it can be perceived as a rewarding response.
The Bad is when an extrinsic reward drives the aggressive and violent behavior, i.e., looting, robbing and even killing for material gain, or when the aggression is simply motivated by achieving a higher social status. This is commonly referred to as instrumental aggression.
Finally, there is The Ugly, the taboo, a behavior, apparently dormant in all men: The intrinsic enjoyment of violence. “The lust to kill is in our blood,” as Albert Einstein put it: “In normal times this passion exists in a latent state, it emerges only in unusual circumstances, but it is a comparatively easy task to call it into play and raise it to the power of a collective psychosis.” 
This ‘appetitive aggression’ describes a lust for violence. It appears in the form of violent computer games, the hunting of large prey, in murder and massacres. In this case, it is not enough to defeat the enemy – the enemy must bleed, must scream.
In the real world aggressive and violent behavior is commonly motivated by a combination of these forms of aggression, sometimes only to overcome cognitive dissonance. As Nietzsche wrote in Thus Spoke Zarathustra: “[…] his soul wanted blood, not robbery. He thirsted for the bliss of the knife! But his poor reason did not comprehend this madness and it persuaded him […] and he robbed as he murdered. He did not want to be ashamed of his madness.” 
 Einstein, 1932, according to Nathan, O., & Nordan, H. (1963). Einstein on peace . London: Methuen.
 Friedrich Nietzsche, Thus Spoke Zarathustra , Cambridge, UK: Cambridge University Press, 2006
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