From what I've seen, it's simply an aversion to mass scale surveillance, even in public setting. The worry being how easy it could slide into a tool used by the state for nefarious purposes (punish political dissidents, etc).
Is there actually evidence of flock being used to stop street crime? I've never heard anything about Flock (or Shotspooter) stopping street crime.
Where I am, the local speed cameras have annual documents about the street their on detailing pre-camera vehicle speeds and fatal (pedestrian) accidents and the decreases in both of them since the usage.
Afaik, the concern isn't that it "could slide" its that flock _is used_ by say Texas to monitor out of state abortions. That isn't solving street crime and certainly didn't benefit the local residents.