If it was that black and white then you better jail 99+% of the population who happens to jaywalk, drive a little too fast, drive past a yellow light, ride a bicycle without a helmet, etc.

Also, why would you want to focus on punishment rather than rehabilitation? The vast majority of those imprisoned are of no danger to society, and the way the US (and most other countries) focus on punishing someone for making a mistake greatly increase the chance that they'll continue to break the laws in the future and become a burden to society.