For more than two decades, Mercury General Corp. Chairman George Joseph has been sparring with consumer advocate Harvey Rosenfield over California’s landmark automobile insurance law, Proposition 103.

They’ve battled in the courts, the Legislature and the media over complex regulatory questions that affect billions of dollars in premiums paid by the state’s 23.7 million licensed drivers.

Now they’re squaring off over a Mercury Insurance-sponsored initiative on the June ballot. Proposition 17 would rewrite state law to allow insurers to attract new customers with discounts, as long as the drivers have been insured for most of the previous five years. But in the zero-sum world of insurance, one driver’s discount must be offset by another driver’s surcharge. California insurance law requires companies to have an approved rating plan based on an average premium.

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