Most of us think of coffee as a morning essential, not a cancer-causing hazard. So the nation got a jolt after a California judge made a final ruling in May that Starbucks and other coffee sellers must inform customers about carcinogenic chemicals in their brews.

The ruling stemmed from a court case invoking Proposition 65, a state law that requires warnings if products or places contain certain types of hazardous chemicals. But the implications reach far beyond the Golden State. Californ