Some of the most convincing evidence comes from American prohibition of alcohol and the drug wars. Basic economic principles dictate that the supply will expand to meet demand. As the demand is difficult to modulate, the strategy of regulating supply has been historically more effective.

The prohibition created a robust black market which all but disappeared when alcohol production came back into the light by legal means. The same logic should hold true for ivory through farming or artificial production (see several comments to this point above).