Phil says "And, the fact that America still leads the world in violent crime raises fundamental questions about whether we're getting it right." The premise is not correct. According to the United Nations world survey (the latest I could find was 2002, so a little dated, but probably still roughly accurate), the U.S. murder rate is 5.62 per 100,000 inhabitants, well below that of lots of other countries. The data are assembled in an easy-to-read graph here . Clearly, your chance of being murdered in the United States is higher than in Europe, Japan, and Saudi Arabia (!), but you would be worse off in Mexico or Thailand.
What is true is that the United States is more dangerous than any other rich country, and maybe this is what Phil meant. But I'm skeptical that one can draw any inferences about incarceration policy from the differences between these countries and the United States. There are just too many confounding variables; empiricists who do cross-country studies of crime, gun control, and the like, are well aware of this. Because the United States is richer than Mexico, it can build more prisons and incarcerate more people. It does not speak poorly of the United States that we imprison more people per capita than Mexico does. Because the United States is wealthier than Mexico is, it can devote more resources to the crime problem. Within the United States, it seems to be true that when incarceration rises, crime falls. As long as violent crime remains a significant problem in this country, it is logical to have a large prison population, though to be sure there are no doubt many ways that prison policy can be improved at the margin.