Social control.

Michael Parenti:

There's really no economic interest involved in it.
They're not protecting the banks!
The police are just doing this because they're on a power trip,
or they're macho, or uh they're control freaks.
That's why they do it. No! Of course it's an economic,
of course they're defending the banks.
...
You see, there are people who believe that the function of the police is to fight crime.
And that's not true, the function of the police is social control,
and protection of property.

He's right, you know.