There's some merit to the claims. Silk Road founder Dread Pirate Roberts designed his service in part to take away power from cartels, which regularly use violence to maintain their grip on the drug trade. An ordinary street dealer could avoid encountering cartels altogether while selling on a larger scale.
However, there are some holes in the study. For a start, it notes that most trades on Silk Road were focused on relatively soft drugs like ecstasy and pot. It doesn't account for violence over harder stuff like cocaine, where dependency and "chaotic" (that is, frequently criminal) lifestyles are larger factors. An addict can't wait for a mail order, for example, and many of the hardest drugs ultimately come from cartels and other criminal organizations. It's also difficult to know whether online transactions were replacing in-person sales or merely supplementing them. In some cases, Silk Road may have just been a way to clear out drugs that didn't sell at the street corner. You'll have to take the findings with a grain of salt, then, even if they do illustrate how criminals can change their behavior when they go digital.
[Image credit: AP Photo/Fernando Vergara]