A lot of the paranoia on Reddit and even HN seems misplaced to me. Federal and state governments already have large fingerprint databases. Most of you probably don't even remember when the police visited your grade school and taught the class about finger printing. Guess that they were collecting. So it's possible but unlikely that the federal government will collect your fingerprint data. However, we KNOW that the federal government is widely collecting communication metadata. This information is a much greater threat to freedom than your fingerprint. Both datasets are identifying, but one reveals a lot of additional information - about your lifestyle, habits, politics, speech, ideas, etc. The fingerprint conveys none of these.
The government has lots of ways to identify you if they want to. Most of these methods of identification are MUCH easier to implement than fingerprints (communication metadata and patterns, face recognition, license plate tracking, etc.). In the end, making a cell phone call is more convenient but less secure than other types of communication, but we accept this trade-off. The trade-off for using a fingerprint to facilitate dozens of daily interactions with your phone seems possibly more favorable in terms of privacy.