Yes, I think you've eloquently summarized my thinking on this. Thankfully I've never had to witness people trying to take justice into their own hands, as you have, though I imagine it must be harrowing to witness especially in a mob situation.
It sounds like you're trying to be part of the solution, which I deeply commend. Thank you also for your very thoughtful reply. It's appreciated.
Retribution shouldn't be the driving force, but I can understand it from a societal standpoint. Victims and the families of the victims will want to see a punishment applied for the harm they've suffered. It's in the state's interest to make sure that it's not excessively applied, but to degree there's a mix of correction and retribution that has to be taken into account at sentencing. One person's spite is another's justice.
I think that if too many people see retribution as no longer being applied, some people will start to take matters into their own hands to seek vengeance.
The state has an interest in preventing that and assuring retribution is applied as evenly as possible, and counterbalanced by other mitigating factors (e.g. the degree of offense, the circumstances under which it occurred, likelihood of reoffending, penitence of the guilty, etc.).