Cooking. Frying or roasting produce diacetyl, acrylamide and all sorts of other potentially toxic substances that don't naturally occur in the food being cooked.

What about fermentation? The production of cheese or bread produces all sorts of chemicals that don't naturally occur in milk or wheat - are those chemicals "natural"? Does your opinion change if I told you that most monosodium glutamate is produced through industrial fermentation?

I'm not against adding chemicals to food. I was just pointing out flaws in the examples.

We should test foods to the best of our ability to make sure they are safe, but I don't think there should be many restrictions otherwise.

Human breast milk naturally contains ammonia, so it does naturally occur in food:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3934511/

(More when the breast is inflamed, which can affect willingness to suckle, indicating there are levels which affect at least palatability)