C'mon man who is dense enough to believe the underground just goes above ground after decriminalization? I know of first hand incidents with "legal" growers in CA and CO not having "enough" so they continue on in the criminal underground and try to "legitimize" the illegal gains through the legal side of the business. Legal or not, drugs will ALWAYS fuel criminal pursuits.
If there’s still an underground market that means the above ground market is too restrictive. How big an issue is illegal moonshiners? Alcohol is regulated but not so much that there’s a large underground market.