I can tell you for a fact that the gunk that comes out is NOT the bentonite! When I did my initial cleanse with Holistic Horizons it did not include Bentonite and I released pounds of mucoid plaque! The mucoid plaque I have since expelled when using psyllium and Bentonite has the very same characteristics.
I agree that you should be absolutely comfortable with whatever you put into your body. I also agree that...for anyone using Bentonite (or anything else, for that matter!)...the source and purity should be taken into consideration. However, you have raised a number of concerns regarding parasites, bacteria, poisoning, cancer and Alzheimer's disease...and yet you are not siting any sources that support these concerns. The history of 'clay' use is a lengthy one and has been shown time and again to be safe and effective.