I agree, a life or long-term prison sentence is far worse than the death. The death penalty is the most immoral punishment that one can give.
Who are we to take someone's life away? It is not our right; even if this person has taken the life of someone else, we should show that we are above their crimes, not at their level.
And, even in the age of forensic science, we cannot be 100% certain that criminals are guilty. What if we were to take the life of some poor, innocent person, and then realise our mistake? We cannot grant life back to them, we have already taken that away.
I am glad we live in a country which saw the inhumane punishment which is the death penalty; if only those nations which still have it could see, such as Indonesia, in the case of Schapelle Corby.