[andrewstuart2]

IMO, you don't even need any arguments beyond #1. Your fingerprint can't be changed and it's public information. You leave traces/copies of it everywhere you go. Just because it's more difficult to read now doesn't mean that technology won't make lifting and reusing your oily prints trivial someday.

Would you create a rubber stamp of your passwords, slather it with oil, and then go around stamping it on everything you own and everywhere you go?

[ng-user]

This is the current case with SSN's in North America. A unique identifier being treated as a password cannot act as a password.