To prove something is safe you'd have to make thousands of people eat it for decades. Short of that there is a selection bias on the test subjects, you also ne

To prove something is safe you'd have to make thousands of people eat it for decades. Short of that there is a selection bias on the test subjects, you also need to know how it goes for pregnant, elderly, children, tourists etc., put them in environments where you're absolutely sure they don't fall ill from other causes and do that until it's clear it's safe, so you need to at least see an infant build a family to know there's no reproductive impact. That would be the minimum level of certainty, and that's just not realistic.