I think this situation, the so called legal pot will be far less of a problem than most people think. Users of cannabis tend to be passive even in the face of violence. Alcohol users tend to be aggressive. Understand that I am speaking in generalities. If the law was properly crafted only the intoxicated improper use of a firearm would be the issue. What a person did yesterday is of no import.
the blood runs free, the rain turns red, give me the wine, you keep the bread