Unfortunately, most of the trade in endangered species is promoted by greed and arrogance. To have a piece of ivory adorning some part of your home or person has been the ideal of many for so long and its rarity makes it expensive.
Rhino horn is used in Oriental medicine, for what I don't know, but I am sure there is something that can take its place.
I did see an episode of Father Brown on TV the other day where they said that chopped tiger whiskers will cut up someone's stomach, this could be a fitting punishment for all those involved in tiger murder and sales.
As I always say when a dog has fouled the pavement outside my house - "They should put the animal down - and get the dog a new home!"