For car rentals paid for entirely by Visa credit cards, Visa usually provides a benefit called the Collision Damage Waiver, which in my experience is pretty good.
It does not however cover personal liability. Are there any insurance companies which offer such additional liability insurance, that will serve as a supplement to Visa's CDW? (The point here is to avoid paying for the car rental company's expensive insurance coverage, if possible.)
To keep this question narrow, I restrict attention to US car rentals. (And, if it matters, Massachusetts.)
Also, I do not own any motor vehicle and do not have any sort of motor vehicle insurance. I do have a US driver's license and a clean driving record. Edit: I rarely drive a car.