Your sarcasm alert shows either your ignorance on the subject or your professional interest in the profit aspect. As you may or may not know, many dentists are profiting from the damage caused by fluorides by replacing the broken or cracked teeth that have been made brittle and prone to breakage.
Root canal work followed by fitting a crown to the tooth's root or a post is expensive by anyone's standards. My last root canal, post, and crown was done about five years ago and cost well over $2000. My dentist tells me that today the same combination of his services and the crown itself would cost roughly 50% more than it did back then.
Cavities form when teeth demineralize faster than they remineralize. It’s a simple process. The bacteria in your mouth eat the same sugars that you eat, but they turn the sugar to an acid. The acids dissolve the minerals (calcium, fluoride, etc) out of your enamel. Your saliva (and fluoridated products like toothpaste, rinses, and drinking water) put minerals back into the teeth. If the minerals come out of the tooth faster than they go back in, you get a cavity.
Fluoride is a terrific “remineralizing” agent because not only is it readily absorbed (remineralized) back into the tooth, it is harder and less soluble than calcium to the acid effects of the decay process. Voila! Fewer cavities.
Your teeth don’t get brittle from fluoride. Fluoride is a much tougher mineral than calcium, and since enamel is made up of 96% minerals, fluoride actually strengthens teeth. It does not weaken them.
If you had a tooth that broke, it is most likely due to the fact that you had a very large amalgam (mercury/silver) filling in the tooth coupled with parafunctional habits like bruxing or clenching. Fluoride didn’t break your tooth.