That's stepping on the jurisdiction of those people over themselves. Everyone is entitled to believe in whatever they want to and live by that. They might die but it's their death, not other people's.
Excerpt that if such people live in a modern society, society bears the cost of such malpractice. And so it behooves other members of that society to at least argue against ineffective practices.
Except if parents refuse to allow proper treatment for their children because of religious or other beliefs, such as being in favour of "natural remedies" rather than lifesaving medicines.
That reasoning would lead you to conclude seatbelts should be optional. Fundamentally, the reasoning goes like this: (a) you have an obligation to protect friends and family from their own bad decisions, and (b) there's no fundamental difference between a friend and a stranger, hence (c) some things should be enforced by law for the good of everyone.
Now that I think about it, basically they should be optional.
One reason their use could be mandatory is that in a crash the occupants might fly out of the car and kill other people if they're not using seatbelts. But I'm not sure how relevant point that would be given that the people are allowed to drive a two-tonne killing machine with very little training in the first place.
However, if we do not consider bystanders, I don't see a problem making use of seatbelts optional. It doesn't hurt to mandate that all cars must be equipped with seatbelts for the benefit of availability for everyone who wants to use seatbelts—which is most people.
Seatbelts do save lives but, again, it's not a criminal offense to commit suicide and fail. So, to think, actually, I find it quite disturbing that they are not optional. I hadn't thought about it before. It's an inevitable slippery slope in that you can't really draw the line anywhere as long as you feel obliged to protect everyone.
Could citizens be forced to eat a certain diet to make them not die of obesity, diabetes and cardiac/circulation problems too early? It's certainly ok to inform the citizens of healthier diets, so that everyone can make their own choices with the best information available. But I argue that in the end everyone is sovereign when it comes to their own life and body.
