You're assuming that the technology works well and that people will understand its limitations and not gradually expand its application. The downside is that t

You're assuming that the technology works well and that people will understand its limitations and not gradually expand its application. The downside is that that assumption is an unrealistic fantasy. Innocent people will be charged with crimes by lazy cops who don't want to do the actual police work of thoroughly investigating suspect lists. There will be juries who don't understand prediction error and find innocent people guilty because they trust the "expert" who says the facial recognition system reported "99.99% accuracy". Some of the 40% of cops who have committed domestic violence will make unauthorized use of this system to hunt down fleeing battered spouses - and this unauthorized use will go unpunished. Innocent black people will be identified as subjects and arrested because of racial disparities in accuracy of these systems. Innocent political activists will be charged with crimes they didn't commit because a cop found video of a crime that the software says plausibly looks like the activist. Every time police get a new tool for establishing guilt, it is abused. The only way to make a facial recognition system that is just is if it is out of control of the police and it can only be used with a valid court warrant - and even then, I'm not sure that I trust the court's ability to control such a system securely.