Feature creep
A lot of workplaces use fingerprint scanners and there is no opt-out.
Needless to say the social security folks are looking into using these as it would speed up signing in and other administrative tasks.
One thing I don't like is that effectively the Police can then say "you're nicked!" if it happens to match up with the one-in-15000 cheap scanner used, so an innocent person can end up locked up for having the wrong kind of fingerprint.
Add to that well known vulnerabilities such as fake fingerprints and we could be in for a rough ride if criminals start copying phones as well.