Had you actually read the article the OP linked, you would see that the drone(s) in question were operated over Los Angeles protests/riots by DHS, not the military. DHS is a federal law enforcement agency. Similar to the FBI monitoring folks.
I'm sure if these "protestors" were peaceful and not blocking innocent citizens on the streets, and no looting was occurring, or police cars or cabs being set afire, buildings burned down, observation platforms wouldn't be so plentiful.,
How does "Spying" come into play. Those "protestors" are in plain sight. What's the difference between a Predator and a Bell helicopter flying above them?