FDA is fighting a fight it already lost. Just another outdated business model fighting something it struggles to embrace. Just like music industry was fighting Napster. Just like US government was fighting for encryption export controls. The information is out there. opensnp, promethease, even google. Anyone can connect the dots and they technically don't need 23andMe to do that. 23andMe makes it easier to consume that information but it is just a messenger.
You say that "false positives" are catastrophic. I doubt that a woman would perform a double mastectomy on itself. She would get second or third opinion from doctors and surgeons. Consider the alternative for a second - what if a women never learned about this risk and died of cancer a few years later.
Consumers will get the information they need one way or another. There is nothing FDA can do to stop it. Tests can be done offshore if needed. The beauty about genetic tests is that you only need to do it once in your lifetime.