Supporters say Prop 17 will lower insurance rates for 82% of California drivers. Opponents ask, why would an insurance company sponsor a measure that might cost it money? Proposition 17 in next month’s election. The ballot says, “Allows auto insurance companies to base their prices in part on a driver’s history of insurance coverage.” Mercury General has put up 10 million dollars for Prop 17, and it’s an auto insurance company. Opponents claim that’s all you need to know.