I can't say I know every detail of the case but I don't recall anyone getting killed or even hurt by Mr. Ulbricht so in my mind the punishment does not fit the crime. IMHO the death penalty should be off the table completely (go Nebraska!) and life in prison reserved for only violent offenders. You can argue that he enabled people to harm themselves but I think that's stretching it. If people want to take drugs, even take too much drugs their going to get it somewhere. If drugs were legal and treatment of abuse the focus instead of punishment Silk Road wouldn't have existed in the first place.
The US War on Drugs is ridiculously harmful and shortsighted, absolutely. But the sentencing is consistent with US policy, however wrong it is. People are getting two-figure sentences for carrying small amounts of drugs themselves. Someone who facilitates the selling of an illegal product on a much wider scale should not get a lighter sentence.
The whole concept behind the War on Drugs sucks, but this sentence is consistent. If it were a shorter sentence, then it'd be similar to the legal inconsistency around cocaine: the form wealthy white people tend to use (powder cocaine) is much less penalised than the form poor and minority people tend to use (crack cocaine), because...?