Maybe it's more a lack of access to modern scientific knowledge than 'craziness'.
This article appears to support you. Letting people know that rhino horn is not medicine reduced the numbers of people wanting to buy rhino horn.
Also, I wouldn't be surprised if it's analogous to the Dr. Oz / anti-vaccine set in the U.S. Those people have access to all the knowledge they could want, but you still couldn't shake their misguided beliefs out of them.
This article appears to support you. Letting people know that rhino horn is not medicine reduced the numbers of people wanting to buy rhino horn.