I'm not surprised that Dostoyevsky's deathless prose takes a while to sink in for a 'liberal eugenicist' like yourself, so here's the conclusion again, pared down and divorced from context because maybe that will help:
No! no! no! No man should be treated so, no man, no man!
No I know what you meant (you smug prick), I just don't agree. I think it's good
that this person suffer. Not everybody deserves to live.
What you're describing is some combination or other of emotional catharsis--which has its place and its uses--and state-sponsored revenge, not justice, which is reconciliatory when it can be and concerned with the prevention or deterrence of future injustice when it can't.
No, what I'm describing is a policy to prevent future "recruitment" for the Cartels. If people learn that the wages of joining the enemy is death, and suffering for their families, then they will perhaps reconsider. The policies used by the Italians against the Sicilian mafia in the 1920's and 30's could be replicated with effectiveness in Mexico, I think.
Also, revenge isn't always a bad thing.
Which means they're the people over whom we're supposed to have some sort of moral high ground.
Pfft. It's not about "moral high ground". It's about winning the war against the Cartels. "Moral High Ground" is for victims.