Natural dangers
I'm often struck by how many people accept an unscientific, unproven claim and then reject the opposite. Vaccines come to mind as a proven and effective way of keeping children safe and healthy. But when a celebrity with no medical experience makes a claim that vaccines cause autism there's a boycott. The result is the deadly spread of a disease that can be tackled with a simple inoculation.
Case in point is the demand for unregulated nutritional supplements and "alternative medicine." The sheer absence of scientific rigor is frightening. There's no doubt that the placebo effect is powerful -- but it won't cure the vast majority of illnesses. That doesn't mean you won't feel better if you take echinacea or garlic for cold symptoms -- there just isn't proof that they're more effective than a placebo.
Homeopathic remedies are even scarier despite their wide acceptance. And often you won't be getting what's on the label even if you think that that's what's working for you. For example, oscillococcinum is a favorite homeopathic cure derived from duck heart and liver. The only problem is that by the time it gets to the bottle it's been diluted to near non-existence.
Lastly, much has been said about the curative effects of the popular and expensive kombucha tea and too little about the dangers. You probably know people who drink this like water to ease their gastric problems not knowing that it's more likely a contributor. Take a look: kombucha