It arguably increased demand and supply for people who are curious to try such things but "don't have a connection".
Street level deals? Violence went down, sure.
But equating the Silk Road to "saving lives and reducing violence" is a martyrdom that, frankly, it doesn't deserve.
And yeah, I was mainly thinking about street level violence. While I've never lived under the influence of a cartel, I have a hard time believing the Silk Road would make anything worse for anyone in that situation. It seems to me giving cartels the ability to directly sell their drug to people over the internet would only decrease violence. Maybe I'm wrong, though.
Based on what? How many OD victims never lived to give a 3 star rating "overdosed, would not buy again"?
You should watch Cocaine Diaries (http://exclaim.ca/music/article/blurs_alex_james_in_bbc_doc_...) - a documentary about a rock star, after talking about cocaine fueled parties, was invited to Colombia and met with everyone from villagers to a cartel hitman. To think that there's no violence in the _production_ alone, let alone distribution and retail, would be naive. And to think that giving the cartels safer channels to sell and increase their market would make those precursors safer is something I can't really picture.
Harm reduction is a big thing on DNM markets and forums. You have information on how to safely use drugs and places to ask for advice. I bet it saved quite a few lives.