Simon, it's simply : supply and demand, when there is less rhino horns and ivory on the black market the prices get higher, and if the prices get higher so also the poaching... So if the trading with rhino horns was legal and controlled the price will be much lower, and the poaching are then much less interesting for the criminals. There is game farmers that dehorning them Rhinos for more than 15 years, and sitting today with 100-eds of kilo of horns, if they can offer them on a open legal market, the poaching of rhino is over !
So to burning this horns/tusks is not very good at all...
Only my two cent...