It will reduce the number in prisons, it's a punishment that fits the crime. It will act as a deterent to those who kill who want to get revenge.
Drug barons are indirectly killing thousands of people by supplying drugs which they could either overdose on, or end up killing others whilst under the influence.
Peadophiles are hurting children physically and scarring them mentally. The majority, if not all, know that it's illegal to have sex with under 16's. If the victim is a teenager who looks older than 16 and it's questionable whether they knew the age, then they should receive a prison sentence- common sense must be used when giving the death sentence.