Scott Morgan spells it out:
We're going to legalize pot, not thuggery. The murderers in Mexico don't possess a single skill that would give them an advantage in a regulated market. Their only asset is a willingness to break the law, and in the unlikely event that they elected to run a legal business instead, they wouldn't be criminals anymore. We will control the regulatory process and there's nothing about marijuana that invites fraud or extortion to any greater extent than every other taxable commodity on the market.
If you're still not getting this, let me put it another way: Mexican drug cartels don't sell marijuana because they're passionate about cannabis culture or botany, or because they love stacking bricks of mid-grade in the back of a pick-up truck. Absolutely the only reason they're in the marijuana business is because we gave them a monopoly on it. When we take that away from them, they will make less money and their organizations will get smaller.