Does painless administration of death render it less harmful?

To kill someone is the extreme act of violence. It should be done honestly if it's done at all. If execution is decreed for a capital offense, let it be done instantly. Bullets, nooses and blades are readily available on the open market and , if not more humane, are certainly more human than administering an attempted painless overdose.
For those who commit the most heinous of murders against the most helpless and in the most cruel and prolonged ways, I have no sympathy whatsoever. If we would be too tender or noble to pull the trigger or throw the lever, then leave that duty to the victim's next of kin.