I was an adult firearms owner before the GCA68 ever happened...there were no "prohibited persons" back then...and there were less problems..
You want crime to do down, repeal the controlled substances act...just like Alcohol Prohibition...it has made many two bit punks very wealthy, caused a lot of crime and wasted a lot of public funds, for what?
Just like the criminals will obtain their firearms illegally if they cannot legally, the people the misuse controlled substances will get their illegally if they cannot legally.
The difference? Does the state get tax revenue on a legitimate sale, or are criminal gangs going to get rich and the state expend serious fund trying to suppress a market that is not going to go away? You better believe the controlled substances peddlers voted against legalizing MJ on CO, OR and WA, and CA last election. If it was legal there would be no money in their activity....the gangs have no funds, they have no lure to help them recruit new members.