Because there are some drugs that make people aggressive, and I personally think these ought to be curtailed where possible. (Again, not a "war on drugs" style curtailment. But distribution, still illegal and criminal)

The first such drug that comes to my mind is alcohol. Its distribution was also criminalized in the past, eventually leading to an increase in organized crime.

What is the most you would pay for a used 2003 Ford Focus, and what would make you willing to pay extra?