Rock
It does not address the quality control issue. There have been a few fentanyl laced cannabis cases, although few and difficult to prove. Well proven is the presence of toxic pesticides and fungicides. 
As a non user I agree with your empathic stance, but it must extend to standard manufacturing quality control as we would expect with every single other product we use in this country. 
And if you don't allow legal sales, there is no tax benefit and you will continue to invite the children of our country to meet the lowest bottom feeders from drug cartels when they are at an age when they are not mature enough to manage it well.