ronburgundy
Contributor
Except that very question is rooted in the wrongful conflating of the law and the outcome one wants in a particular situation. You can have each person deciding what they personally want to see happen in a situation, and at the same time they also defer to formal systems and delegated authorities to determine what the outcome is in any formal legal decision.
I can support laws against vigilante killings, and support that the law should strive to go after such killers. That doesn't dictate my conscience or how I feel (or even what I do) if I see a guy rape and murder a child then see the parent of that child shoot that guy as he tries to escape. If I have that certainty of knowledge in a particular case, then I want the parent to get away with it and even not go through the strain of a trial. That is not inconsistent with (because it is irrelevant to) what I want the laws to be or how I want I want the standard principles of law enforcement and prosecution to be, because those things must strive to operate with consistency to minimize injustice overall, not guarantee justice in any specific case.
But it's the tradeoff in any justice system though. We can make it so that the person harmed or family members decide the punishment. We can make it so the whole country votes the guilt and punishment, or we can have some type of judge/jury system. Humans have a very weird mix of emotions.
No tradeoff is needed because they are two separate things: 1) What the formal system of rules for deciding punishment in general?; 2) What do you want the punishment to be in a specific instance?