Why has crime dropped so much since the early 90s? Criminologists have pointed to longer prison sentences, better community policing, the end of the crack epidemic, and demographics has possible reasons for the decling rate--a trend not even the Great Recession could stop. But one other, less-discussed factor could be that sticking someone up is pretty pointless now, since credit and debit cards have made cash-filled wallets unnecessary, Slate's Christopher Beam argues.

Beam points to a series of incidents in which would-be robbers have left their intended victims empty handed. (Or, as when muggers in Troy, New York, tried to stick up a delivery lady with only a pizza.) "As credit and debt cards replace greenbacks, the odds of a petty thief leaving a job empty-handed are higher than ever," Beam writes. "The prospect of a cashless economy--which some predict could arrive within the next decade--could drive street crime to all-time lows." He explains:

Most violent crime is the result of one person trying to take another person's cash, whether it's an addict robbing a convenience store or one dealer robbing another, says [Richard Wright, a criminology professor at the University of Missouri-St. Louis]. If cash isn't available to steal, the opportunities to commit crimes dwindle. At the same time, the drug trade, which relies on cash at the ground level and drives a large portion of violent crime, withers. Sure, drug dealers can still transfer funds electronically, but only at high levels. Street dealers are unlikely to use credit card swipe machines anytime soon.

But it's not an entirely positive development. The increasingly cash-free economy has given new opportunities to digital criminals, from email scammers to fake ATM keypads that steal your PIN.

And the folks designing these high-tech scams won't be former street dealers. They'll be people with more education and higher income. Indeed, as street crime has dropped over the last two decades, white collar and online crime has gone way up, according to the National White Collar Crime Center. In a cashless world, the crime gap will be even wider. 'Essentially, the rich will have stolen crime from the poor,' says Wright.