Actually, that should not happen. In fact, it should happen less.
This report assumes that legalized prices for marijuana would be 50% of current prices. For cocaine, available evidence suggests that prices might fall to 20% of the current level; for heroin, the evidence suggests it might fall to 5% of the current level. For other drugs, this report assumes that prices fall to 5% of the current level.
As you see, evidence suggests (Feel free to read the study) prices should fall quite dramatically, which makes sense, as produces would no longer have to take on the risk associated, and would be able to produce in larger quantities at a time. That means users would not as often find it necessary to steal to fund their addiction.
Also, in Portugal, the decriminalization of drugs was a success.
Many of these innovative treatment procedures would not have emerged if addicts had continued to be arrested and locked up rather than treated by medical experts and psychologists. Currently 40,000 people in Portugal are being treated for drug abuse. This is a far cheaper, far more humane way to tackle the problem. Rather than locking up 100,000 criminals, the Portuguese are working to cure 40,000 patients and fine-tuning a whole new canon of drug treatment knowledge at the same time.
http://www.businessinsider.com/portugal-drug-policy-decriminalization-works-2012-7with legalization the government saves billions of dollars, and also collects millions if not billions more in taxes. This money, I would propose, be spent on drug education and rehabilitation. It is clear that people are not helped by being thrown in jail, and without the stigma attached to these "junkies" many may be more inclined to get help rather than being forced to stay in the shadows.
We could see a reduction in violent crime, and gang violence, in the US and abroad. Gangs and drug cartels would lose much influence, as most of their funding is from illicit drug trade.