Perhaps the illegal status in other countries contribute to the amount of charlatans that may operate successfully in the Amazon.  Do you think the Amazon had a problem with Ayahuasca charlatans before the days of internet and an influx of tourists to the region for such ceremonies?  The fact that it is illegal most other places creates an environment for uninformed individuals seeking something from people outside of their community, leading to the proliferation of charlatans.  Charlatans can operate because the people that come to them don't know them and are not from their community.  Thats why charlatans are often travellers, seeking "customers" from different regions, or hidden away in remote locations.  

If there were people in our communities legally and willing to perform such things, do you think people would be as interested traveling across the world and putting their lives in the hands of a stranger?  It is in the best interested for the provider in a community providing to members of that community to provide a safe and quality service or product to individuals.  The regulation comes from the community automatically, no government intervention required.  If you have a choice between someone in your community you know does things in a safe and proper manner and one that is more questionable, I think I know who you would choose.  The charlatan will go out of business.

I don't think it is right to regulate anyones ability to use whatever means necessary to "treat" themselves.  I think the best person to decided what someone needs is them self and it is their fundamental right to do as such. 

It all goes back to information.  People that are informed can make the best decisions for themselves.  When something is illegal, it becomes taboo and the information around it becomes less open and reliable.