1. The state isn't sending the soldier to die, it's sending them to fight. They may die, but dying isn't the purpose. The state would very much prefer them to not die, in fact.
2. Nothing bad happens if we just don't kill the serial killer.
The "state" does not have a preference, states are conflicted by nature. Probably would not take much effort to find examples of serial killers who were not killed doing something bad, killing another inmate, killing a guard, getting out on a technicality, etc, etc, etc. Yes, if we lived in a utopia things would be perfect and you would not be ignoring the point.
My definition of utopia allows for disagreement, my issue was with his methods, avoiding the original point and not the disagreement. I never tried to justify anything, at most I expressed a preference for killing serial killers over having wars.