Do you think the paranoia leads to lower crime, via vigilance and reporting? And/or does the actual crime lead to ‘acceptance’ as displayed in the Anaheim boards?
My suspicion is more like allergy theory, wherein if most of your life has no allergens (e.g. no pets, city life) then when you encounter the tiniest of allergens (a suspicious teenager wearing a hoodie) your system goes on total self paralyzing freakout (anaphylaxis).
Good question, and my next one would be "at what cost?"
What are the externalities of services like NextDoor, local FB groups, etc keeping this in people's conscious all the time?
If I had to come up with a hypothesis and test it via the scientific method it would probably be: This is not good as it is a positive reinforcement loop that causes our lizard brains to see danger everywhere/all the time.