It's not about practicing contract law (whatever that means - it sounds like practicing safe non-sex), it's about the state enforcing private agreements so that commerce can happen and people can accumulate property without having to worry that someone with a bigger gun is going to come along and take it from them.
As to the car accident analogy - it would make sense if there were an amendment that said, "Congress shall make no law restricting the speed of vehicles." So then we'd have "car enthusiasts" driving 200 mph wherever and whenever they wanted, routinely running over small children but the response would be "Hey, that's just the price of freedom! We need to protect the right of drivers to drive however fast they want, even though it leads to tens of thousands of unnecessary deaths each year, because FREEDOM. Stop POLITICIZING the TRAGEDY!"