The black market is a natural limit on the &quot;effectiveness&quot; of sales taxes. High enough taxes constitute <i>de facto</i> prohibition, especially for poorer segments of the market. Thus a high enough tax can&#x27;t really be justified by the goals of collecting funds or discouraging vice. The criminal activity is <i>the point</i>; how else could they justify employing so many more police than a rational system of laws would require?