That's the very core of the issue, not knowing what is unsafe. It's not that the concentration of these chemicals increases past what we thought was safe, what

That's the very core of the issue, not knowing what is unsafe. It's not that the concentration of these chemicals increases past what we thought was safe, what changed was our knowledge of his dangerous they are, making current levels unsafe. Any notion for "objectively" deciding these things has to account for unknown information, which means assigning subjective risk to these unknowns. I don't find an "objective" framework a coherent concept because of that. Ignorance of the world must be confronted head on and taken into account, and those that do not incorporate that risk directly into their cognitive models will perform worse at achieving their goals.