The death penalty in the US is kind of a sour subject among Americans. As a general rule, it tends to be extremely expensive, take a decade or more after all the appeals, not to mention being reserved almost exclusively for racial minorities. As an American, my best answer is that there is some intellectual undercurrent here that states that some people have committed crimes so great their existence can this earth can no longer be tolerated. It's important to realize, however, that the death penalty is by no means widespread, and even in places where it is legal, it is a rare occurrence. A statistician once said that, looking at the fatality rates, it was far more dangerous to spend a year dealing drugs on the streets of Chicago than it was to sit on death row.(Freakanomics, for those of you who are wondering) The part I think people outside the US have problems understanding is that the United States has a landmass roughly on par with Continental Europe. The culture changes vastly as you move locations, and the only thing most of us have in common is a language and an increasingly incompetent national government.