Local law enforcement helicopters are the   

You fail to disclose the definition of "Local".  Does the sleepy town of 10,000 warrant the need for a helicopter? Even that depends on the condition of the town.  But when your local mostly peaceful demonstrators don't have enough buildings to burn and they begin to run either on the road or between buildings, perhaps an eye in the sky may be beneficial.  Sure, you could use a drone but even those have drawbacks.  Also, do not forget that there can be periods of time where illegal activity levels experience a quiescent period.  With that do you reduce your force as well?