Reply #4: It's been proven over and over that the death penalty is no deterrent.

[library_max]

Murder one is one of the least recidivist of crimes (unusual cases like Shipman notwithstanding). Most people who commit murder either fully expect to get away with it completely or are so far gone that they don't much care what happens to them. Either way, the difference between the death penalty and life in prison isn't likely to matter to them.

And as other posters have pointed out, the death penalty leaves no margin for error, and yet error is inevitable in any human-run system.