> the chances there is some significant medical harm still undetected is vanishingly small

I don't think this statement is true.

Long-term effects can only be observed over the, well, long term which makes it hard to compare with the baseline. It was measured differently and with very different external factors. Then even if we do by chance manage to observe the harm today it could be very hard to identify the reason — we would see the factual result but neither the process nor the cause.

Take any unexplained health issue we have today, e.g. decline in male fertility estimated at 50% in western counties since 1970s, a dramatic change. Could it be microwaves? Well possibly, can't be ruled out at this point, among many other candidates. Furthermore, with the new research saying that 1) microwaving food in "microwave-safe" plastic containers releases huge number of microplastic particles into the food and 2) microplastic accumulates in testicles — it's not even a fringe science anymore but a normal theory to be studied and be proven or disproven.

Do we have any other health issues that increased over the past 50 years? Yes. What caused them, is it something recent that became popular in the past 50 years? Very likely, yes. Do we know it? Not yet.

It took us a very long time to figure out cigarettes. Or leaded fuel, even though we knew in advance that lead is poisonous.