Wear a seatbelt. Don't fine and/or imprison those who do not.
If not for the law and the fines, the behavior of not wearing it wouldn’t have changed or, if it did, it would take much longer.
Edit: typo
1. I don't like seat belt laws because I don't like people telling me anything, even if it's the right thing to do and I do it anyways.
2. I don't like seat belt laws because I'm a complete moron and don't want to wear a seat belt even though it's the unambiguously, obviously right thing, I don't like the seat belt itself. I may or may not think that other people should or should not also not wear a seat belt, but I'm mostly worried about personally being penalized for not wearing a seat belt.
3. I don't like seat belt laws because even if I'm wearing my seat belt, police can use it as a tool to pull me over and harass me.
4. I like seat belt laws because they encourage everyone, myself included, to do the right thing, and reduce the societal costs that I'd otherwise have to share if other people wear their seat belts.
"Just do the right thing" works for me as an individual, but I'm not just an individual - I am a member of a society, I contribute insurance premiums and tax payments that financially go towards first responders and health care that might be abused by people who don't do something as obvious as wearing a seat belt - not to mention the emotional, moral and ethical weight of driving around people who might be thrown through their windshield and splatter all over you and your car in a crash.
This is one of those positions which seem reasonable and valid from the inside, but from the outside feels like watching an adult throw a temper tantrum when they don't get their way.
To give a wild-ish example: I am very careful about my teeth and I floss often, but I wouldn't like to have to carry around an authorized list of last cleaning sessions for a random cop to check. Even though it could, on aggregate, save quite a lot of money for dental care in our local single payer system.
It's not about the vegetables, it's about handing away more of your agency to those who can and will abuse it.
Tying into the greater point, I think the environmental shaping by the auto manufacturers has a lot to do with the high compliance rate. A lot of work has gone into belt comfort and seatbelt detection systems are calibrated to the right amount of annoying and undergo UX/focus testing.