So prosecute them for those other things, no? Instead of helping criminals grow their business by banning non-harmful stuff and giving them monetary growth opprotunities.

Crime benefits from network effects even more than regular businesses, you have to attack them via every opportunity.

However you are putting words in my mouth, in a typical American style of prosecution-->banning. It is quite possible to legalise and regulate marijuana. American halfway legalisation creates an industry which funds OC and can't be prosecuted. Canadian legalisation creates a revenue source for the provincial governments while providing vertical integration and control, and the volume of illegal weed has plummeted.