Is the perception that we will be nefariously ingesting your private data? Or that FB auth is just a trend? Or just a mistaken assumption that all users actually have a Facebook account?
To me it just seems retarded to assume that everybody have a facebook account - especially when OpenId was invented to solve this exact problem. And guess what, a facebook account is also an open id.
Happily, google is an openid endpoint, and basically everyone has a google account for gmail or something.