Hitch blames God:
The reason why the United States is alone among comparable countries in its commitment to doing this is that it is the most religious of those countries. (Take away only China, which is run by a very nervous oligarchy, and the remaining death-penalty states in the world will generally be noticeable as theocratic ones.) Once we clear away the brush, then, we can see the crystalline purity of the lex talionis and the principle of an eye for an eye.
The Dish 