If you're concerned about privacy, i'd say it's not limited to biometrics. Credit cards are very convenient, but also have a privacy price. If companies like Equifax can get reports, then i assume the government can.
It seems each biometric method -- fingerprint, iris, retina, facial, voice -- has it's own problem. We facial we see that a persons appearance my change over time. Some have high false acceptance and false rejection rates. And in general, if the "super" biometric device can be circumvented, the security system falls.
If i explored this topic more, i'd look into social trust systems. I think another person is the best detector of identities. Like when i get into work, i can have a colleague vouch for me. Of course this won't work in the market.
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