There are many other things to consider when it comes to fluoride.
You can think of fluoride kind of like a cast, it does make the enamel of teeth harder but it's not necessarily beneficial to use all of the time. If you eat a healthy diet and take good care of your teeth fluoride is not necessary. A deficiency of fluoride will NOT cause tooth decay, it is not a nutrient it is a medication.
Recent studies compared children living in fluoridated water versus non fluoridated areas and found little statistical difference in tooth decay rates, further studies have shown an over all decrease in tooth-decay rates in both fluoridated and unfluoridated countries showing little evidence of an advantage in fluoridation. The lower rates of tooth decay are more likely thanks to improved oral care and dentistry practices as well as nutrition.
Fluoride is also toxic. While the amount of fluoride you are exposed to through toothpaste is very small, you may not realize you are also exposed to fluoride through drinking water (even some bottled water), table salt, shower water (you can absorb it through your skin) and in infant formulated milk. The number once source of calls about fluoride poisoning to the American Association of Poison Control are from toothpaste ingestion by children under the age of 6 who metabolize fluoride faster and more instantly.
Chronic over exposure to fluoride can lead to dental fluorosis, skeletal fluorosis (causing sporadic pain, joint stiffness, muscle weakness and fatigue), hyper sensitivity, chronic indigestion, gastric irritation, insufficiency of the renal system, numbness, muscular spasm, birth defects and cancer. Acute poisoning can cause nausea, vomiting, hypocalcemia, hypotension, hyper salvation, metabolic and respiratory acidosis and failure, coma and convulsion leading to death.
Due to these risk factors and the fact that fluoride is not an essential nutrient we believe it should be treated like a medication and only used when it is medically necessary: if one has a poor diet, has extremely bad teeth, suspects they may be forming a cavity, has cracked a tooth or so on, you can buy topical fluoride to be used as a spot treatment in these cases.
You may know someone who looks like they have blotches on their teeth like milk colored snowflakes, this is dental fluorosis which is caused by chronic exposure to fluoride as a child. it is an indicator of chronic fluoride toxicity and is unattractive and avoidable side effect of the over-use of fluoride in our modern world. This is why even the ADA recommends low fluoride toothpaste for children living in fluoridated areas... did you know that they recommend that? Our dentists never told us that.
The fluoride added to our water is not a pharmaceutical grade chemical, it is a by-product of the chemical fertilizer industry. Recent studies have shown Silicofluorides to leach lead from the ground and old pipes leading to heightened chances of heavy metal poisoning.