Why are people against the Death Penalty?

even if someone s 1000 children and brutally kills them (or your own kids), or the worst crime imaginable, some of these people still think its a life worth saving. These people want to fully defend these monsters and give them food, clothing, sheltor, tv, games, like a vacation. Even if they do go to prison, what about parole? Look how many murderers easily got out of prison from parole and did the same thing. Why not give them capitol punishment? Not only that, why is it that over the years, everywhere stated using "humane" methods like lethal injection. Was that criminal who did whatever he did a "humane" thing to do? Why not boil people in oil or remove their skin like centuries ago? and Why do there monsters stay on death row for 30 years knowing that eventually someone will come in and hand them "how would you like to be killed, chose from 4 painless methods" brochure and that they will eventually be systematically killed in a dressed up ceremony and actually get their own grave.