What is the problem with biometrics? Well, the upside is that you can't lose, misplace or forget your body. The bad news is, fingers, hands and even eyes can be removed, whether or not you agree to it. But the problems exist whether or not your body parts remain connected:

The downside is that biometric screening can also work without the user’s co-operation or even knowledge. Covert identification may be a boon when screening for terrorists or criminals, but it raises serious concerns for innocent individuals.

Covert identification is a nice way of saying they're secretly comparing scans of body parts - usually faces - with pictures or scans on file. This may seem like a good idea. In theory you can find wanted criminals this way, but I've never heard of them actually catching anyone that way. Meanwhile we don't know if they're keeping copies of the images they scan or if they are, why. But more troubling than that is the possibility of false positives. It can be a real pain to convince the authorities that you were born and raised in Dubuque when their fancy scanner has identified you as Osama bin Ladens second in commmand...