Biometrics are helpful for identification, but useless for securing anything. As a password it has all the wrong properties. It cannot be changed regularly; you leave it out in the open all the time, its way too simple (most fingerprint 'biometrics' reduce your print to about 10 bits, like your garage door opener code).

See this is another thing that has to be changed in the public perception before biometrics become viable for widespread usage- they're useful for some things but not others, for exactly the reasons you lay out here. They're not a be all end all and immediately solve all problems of both identity AND access management, and they need to be applied judiciously and only when they actually solve a problem.

Some people should watch Demolition Man to understand why biometrics might not be quite as secure as one may think.

In this one particular instance, liveness detection is what keeps that from being a viable thing, as does combining multiple methods of authentication and not just relying on one biometric modality for identification.

Are people desperate enough to chop off a finger to gain access necessarily going to check if there's a liveness detector first?