There is no set standard for fluoride dosing in water, so it isn't possible for you to even know whether it causes harm or not. This is one of the reasons many of the studies have been inconclusive. We should first explore alternatives before just dumping shit into water.
Discussion
Ok, assuming you are correct in what you claim, excuses for why we don't have evidence supporting your position is not evidence for your position. That's just faulty reasoning, and making epistemological leaps for the sake of arriving at a conclusion you prefer.