Research has been done on this subject, and the conclusion of the research is that prohibition increases crime.
Homicide Rates and Substance Control PolicySee also:My research indicates that the theory of the primary cause of violent crime in the United States which is most consistent with the available data is a violent black market caused by the War on Drugs today, and Prohibition in the 1920’s.
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The results of the regression analyses (table 1) support the hypothesis that the prohibition of alcohol or drugs is the primary cause of violent crime in the United States.
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Bruce Benson et al. (1992: 679) performed a cross-sectional analysis of data from 67 Florida counties in 1986 and 1987 to determine if property crime is positively related to the intensity of drug enforcement activities. Harold Brumm et al. (1995: 509) examined data on 57 cities in 32 states in 1985 to determine if homicide rates are positively correlated with the percentage of a communities law enforcement resources that are devoted to the enforcement of drug laws. Both property crime and violent crime were determined to be positively correlated with the intensity of drug enforcement activities.
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The remaining question is what the strong correlation between the homicide rate, the United States’ substance control policy, and, during the later half of the twentieth century the United States’ weapons control policy, means. One possible theory for the correlation between the homicide rate and the substance control proxy is that homicides are caused by drug and alcohol use, and therefore homicides increase as drug and alcohol arrests increase. This theory does not explain the data. I have shown in table 1 that the fit between the homicide rate and the drug use rate is very poor, but this result is of somewhat limited value since drug use data is only available from 1975 to 1997 and none of the other proxies are significant during this time period. The best argument against the theory that substance abuse causes crime is the end of prohibition. The end of prohibition by the repeal of the 18th amendment in 1933 was a political choice unrelated to a change in alcohol use. This political choice was soon followed by a large decrease in the homicide rate. This indicates that the theory which is most consistent with the data is that changes in the homicide rate are responses to changes in substance control policy. I therefore conclude that the best theory of the primary cause of violent crime in the United States is a violent black market caused by the War on Drugs today, and Prohibition in the 1920’s.
Violence and the U.S. Prohibitions of Drugs and Alcohol(pdf)This paper examines the relation between prohibitions and violence using the historical behavior of the homicide rate in the United States. The results document that increases in enforcement of drug and alcohol prohibtion have been associated with increases in the homicide rate and auxilliary evidence suggests this positive correlation reflects a causal effect of prohibition enforcement on homicide. Controlling for other potential determinants of the homicide rate - the age composition of the population, the incarceration rate, economic conditions, gun availability, and the death penalty - does not alter the conclusion that drug and alcohol prohibition have substantially raised the homicide rate in the United States over much of the past 100 years.
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[T]he estimates presented here suggest the homicide rate is currently 25-75% higher than it would be in the absence of drug prohibition.
Are these the same reserchers that show that gun bans work?
I have no doubt that legalization would lead to lessen some crimes. There would be less smuggling for starters. The Europeans are living through a crime wave right now that is growing and growing at an inverse rate to their drug enforcement. One might ask why people in a nanny state would commit such crimes, especially with cheap drugs?