depending on source, Fluoride is the 13th - the 17th most abundant element in the earth's crust... predominantly paired with calcium. You likely will not find ANY life without at least some fluoride in it, in one form or another... whether it is considered necessary or essential could be debated ad nauseum, in part, due to life being able to substitute one element for another if need be in the absence of the preferred element, AND the body's ability to buffer, to a certain extent dependent upon health, too much of one element or another.
The problem is that humans, "WE" have concentrated some of these elements, such as fluoride, lead, aluminum (The 3rd most abundant) etc... for any number of reasons and convenience and our bodies can no longer "buffer" them as we would be able to in a "natural" environment...
WE are challenging our very survival. I think that most people into natural health may know this, but do not understand it.
In other words, you cannot hide from so called "undesirable" elements at all... all you can do is avoid exposure to man made concentrates of them. The reason they are a problem at all is our own doing to begin with and NO one, not even us the "consumer" is willing to take responsibility for our actions...
Choose what you purchase wisely, and some of the undesirable products could fade away... however, be sure to understand that so called "greener" purchases, many times are not.