Car-sharing is a utopian idea. Several companies are trying to build ways for people to rent out their vehicles to others for an hourly fee, and they all say they’re doing it for the best reasons—to let people make extra money from an expensive possession they’re not using much, to save the world’s resources, to bring neighbors together in mutually beneficial transactions. Peer-to-peer car-sharing also assumes the best of us. Only in a world in which people are fundamentally good—in which I can be pretty sure that you won’t trash my ride just because it’s not yours—would this scheme work. Finally, these businesses imagine that the government and insurance companies will be forward-thinking enough to go along with the plan, too.