That is what indemnification is. In the ordinary course of business, if you are uninsured and the rental company's policy is primary and pays out on a claim, the rental company's insurer (or the rental company is it self-insures) would seek indemnification from you. But, in states where this is prohibited by law, it can't.

Bear in mind that this is minimum coverage, typically in the range of $25K. That is a pittance if there is an injury. A judgment against you is good for 20 years. Whether you purchase the single use supplement or an annual policy depends on your usage pattern. But, skating by on minimum coverage is not a great way to preserve equity in your house, investments, and future earnings.