Question

Should cameras on drones watch all public spaces to prevent crimes or is that a violation of privacy?

Answer 1

if drone's camera used for positive purpose just like in prevention of crime then it is not violation of privecy

Answer 2

It should but except in the public washrooms.
However, even at public places it wouldn't be comfortable to all because of its noise, wind blowing and its roaming all the time.
Therefore cctv cameras is a better option.