In America recreational drugs are valued 100x compared to countries where it is legal. What if the price of rhino horn dropped by a factor of 100 because you can now buy it at a pharmacy? Would poachers still risk their lives to get hold of it? Would the allure of rhino horn not dissipate when it is freely available? Grapes and mangoes were at some stage considered aphrodisiac, just because it was rare and exotic. Now these fruit are common (and we don’t want the same for rhino), but it is because these fruit have an actual consumption value. Rhino horn’s consumption value lies in its exoticism. Maybe we can disrupt the whole market by making it legal.
I don’t know if the legalization arguments carry any weight beyond hypothetical, but with prevention of rhino cruelty as a common goal, I believe we should at least seriously consider it.