My point is that testing toxic substances on people without any reason to believe that they will have any effect beyond further damaging their health is, y'know, bad. Obviously. We don't stab people in the head to cure their personality problems, even though brain damage can and has altered peoples' personalities. Have you read HPMOR? Because Dumbledore makes a similar suggestion, but at least he has the decency to suggest something merely inconvenient.

Probably that we have a causal model of how bleach is bad for you, and a causal model of how cancer drugs can help, and bleach would just kill you. We're not evolution, we don't have to test every design before building a car.