Fluoride in water worries some people extensively.
Sometimes we buy fluoride poisons in;
The deadly COX-2 inhibitors provide excess fluoride to kill nerves nerves, no nerves / no pain, leads to permanent nerve damage, inability to walk. Better pain medicines are available, avoid.
Excess fluoride harms the brain so that we cannot think. Nerve damage leads to a host of side effects, personality changes, mania, seizures, bleeding, suicidal behavior. Long term use is never good.
Excess fluoride is not healthy yet some chemo-drugs use fluoride as the active agent, big dollars for anti-cancer fluoride therapy, it makes us sick but limited exposure. There are a vast collection of chemotherapy drugs, some are beneficial, some are not. Short term high fluoride may have benefits.
Plants do not require fluoride and so absorb little from the soil.