People are motivated by numerous factors and may commit crimes for both physiological and practical reasons. A brain tumor can be the cause of behavior that crosses the line between legal and/or socially acceptable and illegal and aberrant conduct, as can the ingestion of certain types of drugs, whether legally or illegally procured. A normally law-abiding individual might be motivated to commit an illegal act out of desperation—for example, severe financial pressure—or out of vengeance for a perceived wrong committed against them. With the so-called “insanity defense,” the defendant in a criminal trial argues (or, more accurately, their lawyer argues) that the individual on trial did not understand the difference between right and wrong due to diminished mental capacity or delusional tendencies.
The literature on crime is voluminous and diverse. Study organized crime and you will encounter multitudes of individuals motivated to commit crimes out of a belief that it is a better way of making money than working a regular job. Study the culture within outlaw motorcycle gangs, such as the Mongols, Hell's Angels, Pagans, Bandidos, and so on, and you will encounter thousands of individuals who simply love the outlaw life, rejection convention and making money through trafficking in drugs, weapons, or people (i.e., human trafficking). Journalist Pete Earley spent a year interviewing and observing inmates in a maximum-security prison for his book The Hot House: Life Inside Leavenworth Prison. The real-life inmates interviewed and studied by Earley represent the spectrum of criminal behavior, from those who reject the law on principle and accept prison sentences as the cost of doing business, and those whose lives are spent in and out of prisons because they lack the mental capacity to make “rational” decisions.
William Queen infiltrated the Mongols Motorcycle Club as an undercover operative for the US Bureau of Alcohol, Tobacco and Firearms. Early in Queen’s memoir of his time undercover in this extremely dangerous criminal organization, Under and Alone, Queen, operating under the pseudonym Billie St. John, describes a conversation with a member of the Mongols who has befriended the undercover law enforcement officer. During this encounter, the Mongol informs “Billie” that the Mongols are an outlaw organization and that he, the Mongol, commits acts that can land him in prison if caught. The purpose of this confession of sorts is to ensure that the prospective motorcycle club member, Queen, understands fully that, if accepted into the gang, he will be expected to commit serious crimes. That is the life one chooses if one wants to wear the coveted symbols of this organization.
The purpose of the above paragraph is to illuminate the extent to which many criminals are motivated by a desire to live outside the law because they find life within the constraints of “proper” society confining and not much fun. La Cosa Nostra, the Italian American network of criminal organizations popularly known as the Mafia, is full of individuals who make considered decisions to life the life of the criminal. It is not just organizations. Thousands of individuals similarly make such decisions. Are these individuals somehow physically incapable of making “rational” decisions? In many cases the answer is no.
On the other side of the spectrum are those who do act out of an inability to understand distinctions between right and wrong or to control their worst impulses. Such is the case with many serial killers. Prisons house many individuals who committed crimes because they were driven by some internal mechanism. These people may taunt the police through demeaning letters to newspapers or deliberately leave clues at the scene of a crime out of a desire to see whether police can accurately assess the significance of those clues.
In conclusion, there is no one answer to the question of what drives people to commit crimes. Kleptomaniacs are driven by a need to steal that may originate in the functioning of their brain. Spree killers might be motivated by mental breakdown brought about by major psychological trauma or a desire to gain fame. And, as noted at length above, many crimes are committed by people who know exactly what they are doing. They may believe they are too smart to get caught, or they may not care whether they are apprehended. Most white-collar criminals are driven by greed; is greed the result of a physiological impairment or simply a failure to live within constraints of conventional society? Was embezzlement carried out due to financial pressure or simply so that the perpetrator could buy a larger mansion? All scenarios and conditions may apply.