Limiting the polices technology and resources is an argument that doesn't make sense to me. Especially coming from open source advocates. Smells of hypocrisy.
Innocent until proven guilty, and police gathering evidence of a crime and scene to find, catch, interview and potentially prosecute a suspect. If that proves more expensive, spend enough on policing to achieve adequate deterrence and conviction rates.
The problem with any mass trawl or systemic facial recognition is it makes it utterly trivial to abuse the rights of those who happen to be in a minority group, or to actively look for crimes with which to persecute someone disliked. This is policing the wrong way round.
I hold just the same views about traffic enforcement. Cameras and automatic fines worse than a police officer in a patrol car. The officer can let someone off with a chat if there were clear extenuating circumstances - cameras can't. The officer can catch bad or dangerous driving that happens to be at legal speeds - cameras can't.
I see no hypocrisy here.
People want justice, but they also want individual liberties to not be violated. Particularly in the US the Constitution is filled with stuff to keep a government seeking 'justice' from getting out of control.
You know we have the technology to monitor people location and conversations in real time, we can put those monitoring bracelets on everybody , promise not to use them until a crime is happening and we want to see who was where.
This will solve crimes but it gives a big oppressive tool to the state, is your point that all possible tech should be used if is not too expensive so we reduce crime to 0? This may mean cameras on private properties, mandatory personality checks, social score etc.