You guys are honestly naive if you think facebook doesn't know who you are. They don't need to do KYC, you already gave them more personal information than what they can get from your ID. They know your friends, families, topics you're interested in, location, and much, much more.
Not really. FB only know about you from the information that you chose to feed. For my part, I have never used my phone number or regular email ID for registering for Facebook. But you may be right in certain aspects. They can get information about location, IPs, friends/family.etc. But that is different from knowing your social security number or having access to the tax returns.