Look at Texas and Alaska, the two states with the most gun toting folks, and crime is way down there. Here in Maryland, we have the revolving door of justice. Look at the police blotters, I would guess 75% of folks arrested have many priors.
What about Detroit, Phoenix, Orlando, Atlanta and Dallas? All shall issue states. I'm sure I could think of some other cities with high crime stats which are also shall carry states. If you are going to argue shall issue, stick with the constitution because those other arguments make you look stupid.