Imagine a hypothetical law which arrests anyone who trades in red shirts. Someone comes along and doesn't see what the big deal is and decides to trade in these shirts on the black market. Lives are saved because it is impossible to get shot at while paying for red shirts over the Internet instead of in person. Then the dude who ran the red shirt marketplace and seems like an opportunistic idealist gets locked up with the key thrown away.
Anyway, it is arguable that the Silk Road saved lives, given that black markets are persistent regardless of legality.
https://cybercrimejournal.com/pdf/Lacson%26Jonesvol10issue1I...
https://gwern.net/doc/darknet-market/silk-road/1/2013-vanhou...
The idea of looking at someone's motivations to determine their sentencing is critical to our legal system - otherwise important defences like the "Battered Wife Defence" wouldn't work.
I think most of us can also see a difference between a poor person stealing some gloves to stay warm in the winter and a rich person stealing those same gloves for the thrill. The only difference here is you don't like the fact that Ulbricht's motivations were more high minded than your average crack pusher (cough CIA cough) - the judge didn't either - in fact he sentenced him harder for it to make an example of him.