[throwaway8689]

Assuming you are not being disingenuous: there is a trade off with a lot of uncertainty - other things are also implicated in stomach cancer, and at the same time untreated dental disease causes other health problems too.

But I prefer to rely on brushing my own teeth and avoiding certain foods to maintain my own health, rather than have a medication added to my water supply because the guy next door does not take care of his health.