Look at it this way: 99% of everything men have ever know has been wrong. All scientific theories (except the current ones) have been proven wrong. And, at every point in history, men who thought the current theories were wrong were labeled heretics or morons. There were men who wouldn't let themselves be 'bled' 200 years ago and men who won't undergo chemo today. And that is their choice.
I think a lot of people make stupid choices, but if it only harms themselves, I say let them. Hell, I would have thought some of Bill Gates' decisions early in Microsoft's history were wrong, but that goes to show what I know.
Every person should be allowed to make their own decisions (and live with the consequences of thereof).
If someone believes in homeopathy or the new age panacea du jour over real medicine, let them. If they die because they made the wrong choice, it's a shame, but at least they died free men.