Because black markets for these goods are much more devastating to the animal populations than a legal regulated marketplace.
I can see that there is logic to both cases. Saying one side is "simply not true" doesn't make your case. Is there any firm evidence either way.
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).
Your turn.
http://www.bisbeesconservationfund.org/conservation/savether...
The wisest thing to do would be to give it away for free to anyone interested. That would ruin black market.
It is not about changing the world overnight, it is about moving 1 inch every time.