When I lived in California I saw one of those prop 65 cancer warnings on a loaf of bread.
Apparently burning toast can generate trace amounts of acrylamide.
This was enough to convince me a subset of these people are complete lunatics.
That shouldn't be enough. Have you considered that the authors of the law did not foresee the issues like those you mentioned? And struggled to either find ways or prioritize finding ways to better communicate risks?
Note that the state did eventually modify the communications that the law required.
https://oehha.ca.gov/proposition-65/crnr/proposition-65-clea...
Prop 65 gets a lot of shit, but the way it is implemented makes a reasonable amount of sense. If there is evidence that the substance causes harm, it gets listed and companies producing products that contain it have to either notify consumers that it is in there, or they have to demonstrate that the amount of the substance does not cause harm (there's a very low general threshold and some specific thresholds that are higher).
That leads lots of companies to go the low cost route and use the notification safe harbor, but it also creates an incentive to find alternatives and so on. You get cases like you mention, but the alternative to the evidence based approach is to hand wave that it's not harmful.