Does keeping drugs illegal limit availability? Probably to a degree, but users have to come up with money for the drugs which leads to petty crime in most cases, doing anything they can to get $25 bucks for whatever., theft, prostitution, joining gangs, ... The gangs control the trade obviously, and fight for turf, leading to drive bys. The users still get stoned, hooked, devastated, etc.
Who are we protecting here? What are the repercussions to all this effort? Is the effort worth the expense and secondary ramifications?