The vast majority of Facebook users won't have the technical background or interest to learn about the insides of Bitcoin, but if only a small percentage of them can take the time to do it it will be already something huge.
The majority of the Bitcoin users are also not very tech savvy. Out of the 100 million users, at the most 5 million or 10 million may be knowledgeable about all the aspects of cryptocurrency. The remainder may be knowledgeable about the basics such as how to store and how to send coins, but if you ask them about double spend or 51% attack, they may not be having an answer to those questions. I guess the same situation will be faced with Facebook. The idea of crypto is going to be completely new for the vast majority of the users.