This is a very naive view. Pretty much everything is poisonous at high enough dosages, but there are plenty of poisonous chemicals that are not immediately harmful at low levels.

You can have a restaurant, a food manufacturer, a water utility etc. contaminate (intentionally or otherwise) their product with low doses of chemicals that over time will cause health issues or even fatalities.

The marketplace itself cannot regulate such abuses. Even if such contamination was punishable by law, the time lag would ensure that consumers would not realize the impact until long after, perhaps even after the statute of limitations has expired.

Just look at third-world countries to see how the lack of regulation works out. Or China.

> ... I suggest changing you patronage to a better place.

I don't know whether my restaurant has rats in the kitchen. How could I? The entire point of health inspections is to find out what the consumer cannot possibly find out themselves.

> Why do you think everybody else can't do the same?

Trendy, swanky restaurants are routinely shut down for doing very bad things behind the scenes. So clearly they can't.

Companies don't work for you; they work for themselves. If they have no incentive to be good, they usually won't be good; because, say, it's less expensive to be highly hygienic. You just have to look at the literature of consumer abuses to see how companies will continually, eternally act for their own good, at the detriment of consumers.