That is true of any human. Comparing cultural differences and human nature are completely different.
First, to understand their reasonings, abandoned all you know about Western medicine and read up on traditional medicine and folk medicine and how they developed. Western medicine is not always the best, nor is traditional. In order to understand the property linked to some of those traditional cures, a scienitific study must be held and extract information out of it. However unfortunately because of their long history, a lot of those cures have spiritual connections as well.
Shun them all you want for destroying their native population, you cannot defeat people's rationale behind the purpose of taking those procedures.
I remember a segement on TV where they were trying to protect a rare Asian sturgeon, however people keep harvesting them because the surgeon has a spiritual connection with the local medicine. What they ended up doing is isolating a small population of sturgeon in a government program for aquacultural purpose and they are attempting to breed and restock the rivers.