...but if I did, I'd make it as entertaining as possible.
I do not believe that any human being is justified in taking the life of another human being. The death penalty does not make sense if you're an atheist, and it doesn't make sense if you're a theist. If you are an atheist, then you probably don't believe in an afterlife. In that case, you are depriving the murderer of existence without inflicting any form of punishment. Since all humans do eventually die, the murderer will die of natural causes eventually. Why not inflict as much punishment before then? Execution robs you of that. If you are a theist, then you probably do believe in an afterlife, which means a "hell" in which the wicked experience divine retribution. However, once again, if you execute a murderer, then he or she will go straight to Hell. And if you do happen to be wrong about the whole "God" thing, you've let that murderer off the hook. Now, since there is a zero per cent chance of the murderer living forever, then it makes sense to inflict as much temporal punishment as possible, then let the murderer experience eternal damnation upon his or her death.
So that's my position on the death penalty. I wonder though, why is the modern form of execution (i.e., lethal injection) so humane? If the person being executed is truly terrible enough to warrant death, why be nice and quick about it? Moreover, he or she has inflicted so much psychological damage to society, and he or she won't be paying taxes anymore, so we might as well milk him or her for as much as he or she is worth before executing this person.
To that end, if I were in favour of the death penalty, I'd like it to be as fun to watch as possible. Maybe we should do it the way the Romans did, and feed people to lions. Think about it. In our capitalist society, there'd be a new niche market for lion tamers to train lions to eat people on command. There's the entertainment value of watching someone being eaten by a lion--hey, the government could even charge admission and recoup some of the losses from killing one of its citizens. The families of the victims could receive complimentary videos of the execution--fun for the entire family!
A humane death penalty is hypocritical.
And yes, if I were a lion tamer, I would like a nice big hat that says "Lion tamer" in bright neon flashing letters. And now for something completely different.