First of all, we love partitioning people into good and evil sets. If we can only root out and imprison the evil people (and, btw, give all the good guys guns), there would be negligible crime.
Secondly, we believe punishment fulfills justice. Despite well documented issues in applying the death penalty equitably, or even solely to guilty people, we maintain that heinous crimes must be met with human sacrifice.
And to be honest, I think human sacrifice is literally what we believe in. When something goes wrong, we require someone to feel pain. The more permanent that pain, the better. This goes beyond crime. Look how sports players are immortalized for their blunders. Look at the mob justice of the Internet. Look at how we crack down on the vulnerable when the middle class struggles.