You can tell when fruit goes bad. Spoiled fruit has built in warning signs, such as putrid smells, deterioration of skin & visible molds. People, on the other hand, don't come with such nifty warning signs. They can appear to be totally "normal," when in fact, they're really insane & irrational.
Unfortunately, we have to suffer having "food poisoning” in order to know that it's not healthy for us.