I'm not entirely certain that black markets are the best way to facilitate a safe drug trade, but given a choice between Silk Road and more violent alternatives, Silk Road seems like the obvious better choice.
Right. Aside from, or in spite of, being a black market (by necessity), Silk Road was pretty benign compared to the alternatives. Surely Silk Road was taking some profits away from drug cartels. Probably not much, but a legal market would put them out of business. Now with Silk Road gone, all that trade is back under the umbrella of the cartels again, and the profits are theirs.