It will give the consumer the option of buying the product from a legal, ethical, controlled source.
At present, all trade in rhino products is illegal. Sentences and risks for poaching offences and illegal trade are high. Many poachers have been killed by anti-poaching forces or police and many illicit traders have been imprisoned for their crimes. The risks involved in obtaining rhino horn are a substantial factor in the inflated price of horn.
Enabling the consumer to buy horn legally, from rhino that have not been killed, will undercut the Black Market and will give the consumer the option of buying horn without the attached risks and probably at a much better price.
Currently, rhinos are being killed because their horn is valuable. If trade in horn were legalized, rhinos would be worth considerably more alive than dead and the incentive to protect them would be very much greater.
There would be no need or desire for anyone to kill their rhinos.