Ah yes, the tired old saw... "Isn't killing someone for murder hypocritical?"
First off, your proposed solution "Lock them up for life" is also a "death sentence", it's just the cowardly way out of it. Keeping people locked up for life ultimately costs the average citizen more than any kind of capital punishment. So great, we have here someone who has decided he didn't want to live by the rules of society and instead of making the criminal pay for it, society does instead.
Second, I just love all the gentle hearted people crying about the criminal. What about the victim? What about their rights? The big difference between the criminal and the victim here is that the criminal is still alive. Just because the victim is dead does not mean we should forget about them.
Third, all the bleeding hearts in the world have made prisons more like a long holiday than an actual deterrent. If prisons were places that actually punished the people in them, then maybe we wouldn't have to send as many people there. Sure, you get locked up, and possibly raped repeatedly, but you get taken care of, all at the taxpayers expense. The farce that is the death penalty is also not much of a deterrent these days. How many years and how many tax dollars are spent before the sentence of death is actually carried out?
Fourth, the old "what if you execute an innocent argument". What makes you think that there's any realistic way that any government would be able to compensate someone they locked up that long?
The death penalty isn't uncivilized. What is uncivilized is letting all these people who don't care about the community, or have any respect for the people they live with locked up and making the society pay for it all. Not only do they not contribute to the society, they feed it on it, sucking up tax dollars like a parasite while not have to do anything at all.
Society takes better care of its criminals than it does to the law-abiding people that live within it. How can you possibly call that "civilized"?