Luigi is a symptom of an overly inactive justice system, if you don't prosecute crimes then some people take the law into their own hands (as a matter of fact). Preventing vigilantism is why having a working justice system is important to a functioning society.

DPR is according to his defenders a symptom of an overly active justice system prosecuting crimes that shouldn't be prosecuted. Though I'm not sure I personally agree with that.

OJ was just a crook.

I don't see how those are remotely comparable, the OJ people believed he didn't do it and was set up by the racist LAPD while the Luigi people think that what he did was good actually. I guess the Ross Ulbricht people are more like the latter but they still seem pretty dissimilar.