I am a Conservationist and D.M. has got it all wrong. Protectionists and Animal Rights groups are opposed to this auction, not TRUE Conservationists. 
Sustainable utilisation is the right way to go.
John Hume is entitled to sell the horns he has legitimately harvested from the rhino under his protection, at enormous cost to himself, not the tax-payer. Money goes back to further encourage other land owners and communties to realise the rhino is a true assett, to be treasured and defended. 
It is the only way the species can survive, in this complicated (and frequently corrupt) world.