The point is they will find something else ILLEGAL to do. they won't go straight. So that part of your hope is bogus.
When alcohol prohibition ended the national crime rate declined dramatically. So whatever pursuits the displaced booze dealers followed the statistics do not support the theory of continued criminal activity. While some undoubtedly will follow other illegal pursuits there is no reason to believe that all or most would.
While I have no opinion on the potential legalization of all presently illegal drugs I strongly advocate the legalization of marijuana, which I believe to be relatively benign. And if marijuana were legalized the demand for it would not decline, meaning the need for experienced growers and distributors would remain constant. The major difference would be the federally mandated requirement to produce and distribute quality cannabis products, which implies the creation of a new tax-producing, jobs-producing industry.