They offered us the choice to ride it with or without the seatbelt. (Ours didn't have the co-pilot seat for the dummy, so I guess we were the dummies.) Only if you didn't use the belt, you had to close your eyes so you wouldn't know exactly when you would hit. I already wear seatbelts, so all it convinced me of was that it would hurt even with belts at only 20 mph.
But as for using it to convince people to pass the law ... Wouldn't it be better to have them at every testing location and make people ride it before taking their test? I don't need a law to tell me to wear a seatbelt, any more than I need one to tell me to wear a helmet on a motorcycle. Just like I don't need a law telling me to bring oxygen if I try to scale Mt. Everest. (Not that I'm about to try.)
In general, I don't like laws that exist solely to protect me from myself. Demonstrating how important seatbelts are is IMO the way to encourage their use. It should not be a way to convince someone to pass a law.