You are covered by your own liability insurance, as most policies are written. Same as for your own car.
What they are trying to sell you is Collision Damage Waiver, i.e. the rental company will not try to collect from you the difference between what your insurance covers and what they want for the damage. Rather than insurance, it is a fee for waiver of liability. At $24 a day, it can't be an insurance premium, no state insurance company would permit a $8760 premium for so little risk. CDW is a contract feature, not insurance.
Whether or not you want the CDW depends on your own insurance situation, as it can be worthwhile is your own coverage leaves you with large personal risks (a whole lot depends on the size of your deductible).
When I traveled on business, the policy of our (self insured) company was to decline CDW. On my own, I declined the coverage when I was paying by American Express, because it was their policy at the time to insure most of the difference in liability. Other credit card companies have jumped on this as a sales feature for various premium credit programs, so figure out how you are paying and what your credit card plan does for you.
You probably want CDW if you are paying cash for the rental, but who lets you pay cash today?
Tom Test
Itasca Spirit 29B