The symptoms of heavy metal poisoning, esp. at low levels, are often subtle and can be confused with those of other illnesses and conditions. How can they be so damn sure that mercury fillings are safe? Things like mercury and lead are dangerous partly because they have no beneficial function in the human body at all, and we and our ancestors never evolved means of dealing with them, because we were not exposed to significant levels until mining and industry began releasing them a few centuries ago. They are not like other metals, e.g. iron, which occurs naturally in food and water, and is necessary in appropriate quantities.
Excellent posts.