Zimbardo, Phillip G. The Human Choice: Individuation, Reason, and Order Versus Deindividuation, Impulse, and Chaos, In W. T. Arnold and D. Levine (eds.), Nebraska symposium on Motiviation, Vol 17., 1969.
"When a man exercises his volition, chooses to commit himself to a course of action, and accepts personal responsitiliy for its consequences, he distinguishes himself as unique among living creatures and calls into question our laws of behavioral control"
"In the process of having to generate intrinsic justifications in order to make a discrepant commitment appear rational and consistent, man shifts the locus of contorl of his behavior from external stimul to internal cognitive controls."
Consistency, Rationality and responsibility are prized in society. "The act of freely making a commitment for which one assumes responsibility individuates the decision maker".
But the world seems to be acting otherwise. People are excercising control to destroy themselves and others.
Festinger showed in the 1950's that there is a "reduction in inner restraints" toward expression of counter-norm behavior when individuals are 'submerged in a group".
Ziller proposed that "individuation is desireable withing a supportable social climate, but deindividuation is sought as a defense against a threatening environment." Deinviduation results in a lowering of the threshold for expressing inhibited behaviors.
If one has been inhibiting a certain pleasurable behavior because of social norms, a lowering ot that inhibition could trigger the start of the behavior which would continue until some other outside force acted on it.
Traditionally, festivals and parties have served for people to "blow off" destructive tendencies by lowering inhibition a bit. Future thinking and responsibility reduce urges for immediate gratification. History and logic force us to perceive continuity and rational consistency, legal systems impose responsibility and liability.
Anonymity (lack of criticism by others) should reduce inhibitions of behavior. The inhibiting effects of responsibility can be reduced if the behavior is done by a group or if another accepts responsibility.