> If a substance already exists in nature and has been in use for a long time, then it's reasonable to take the position that it is probably within harm limits.

Reasonable, but wrong.

Simple case: Did you know that occupational sawdust exposure is strongly associated with cancer in the paranasal sinuses and nasal cavity?

There's also some pretty compelling evidence that coronavirus's (so common cold & flu) are associated with dementia/Alzheimer's.

Alcohol increases cancer rate more than some of the "chemicals" people will complain about. So does Bacon. So does sunlight.

All of which have been floating around in Human contact for a LONG time.

Again - we do a pretty good job at filtering out the stuff that's fast acting and harmful. It's just really difficult to tease out information that requires long term monitoring and involves small/moderate increases in risk.

Think about how long it took us to figure out that lead exposure is really nasty. We used lead for thousands of years prior, and it's literally a base element.

---

As for

> Also, if a chemical is known to be toxic, then rigorous testing should be performed before allowing it to be widely distributed and used.

No one is arguing otherwise, and normally large and expensive studies are done on short term harm (extensive animal testing). But you tell me how we can reasonably and ethically do longitudinal studies on large groups of humans to determine if a new substance is going to cause small/moderate cancer rate bumps over 50+ years?

This is just genuinely a difficult problem to address, and it's not simply like we can go "wait 50 years and see"! Because usually we're trying to use these things to address existing problems. Ex - pesticides and fertilizers might still be net positives even with the cancer risk - do we avoid them and let people starve today? Or feed everyone now and have a 10% bump in cancer rates 50 years later? There's no golden ticket here.