The problem for deterrence is not severity, but certainty. You can put people in prison for 20 years for jaywalking, but as long as the certainty of receiving that punishment is low, jaywalking will continue. Now insert burglary, robbery, etc. Now stop there. Don't insert many violent crimes. Deterrence requires a rational cost-benefit calculation that is missing in many violent crimes. Guess we're out of luck in that department.