The brushing thing is safer cause you don't swallow toothpaste. The fluoride is absorbed directly by your teeth and very little into your blood stream/brain/kidneys. So it helps strength your teeth without all the brain damage.
But i do agree with you that fluoride is not safe in the water supply at all.
Sidd
the absorption is greater through the gums and most tooth pastes are a good 1500ppm! much higher than tap water and it NOT good for your teeth in any way mate, fluorosis (sp?) isnt pretty