So your argument is that you can substitute any issue in place of drugs? Nice try, but the argument is not as generic as you suggest.
You can put a murderer in prison and deny him his next victim. There is no evidence that gun use is the result of chemical dependence, but volumes of data exist that support genetic predisposition to chemical dependency. There are legitimate uses for guns, while there are none for heroin and cocaine. Gun use directed at humans is a crime, and no one, not even gun owners, has suggested decriminalizing murder.