The topic is considered by New York Times correspondent Al Baker, here, in an article titled "When the Police Go Military".
RIOT police officers tear-gassing protesters at the Occupy movement in Oakland. The surprising nighttime invasion of Zuccotti Park in Lower Manhattan, carried out with D-Day-like secrecy by officers deploying klieg lights and a military-style sound machine. And campus police officers in helmets and face shields dousing demonstrators at the University of California, Davis with pepper spray.There are things to be cautious about, like no-knock searches. But, by and large the police do an excellent job. And, the Lowell Police seem to know their job and are polite. I was recently talking to an Officer at one of the National Grid migrating construction sites and asked about photographing police in action. He gave the answer every red blooded American Citizen should want to here. Perfectly legal.
Is this the militarization of the American police?
Back to the article, it is a bit over the top, but Citizens need to pay attention to all aspects of government, and offer fraternal correction when something is out of whack.
In the mean time, here are some comments from Mr John Sullivan, involved in Law Enforcement out on the Coast:
This essay raises important questions about police force structure in an era of hybrid threat and global protest. The police need to remain firmly grounded in the community and build all capability from community policing.  That said, high intensity crime (gangs, private armies using grenades and infantry tactics as seen with cartels) and terrorist attacks (like Mumbai-style 'swarming' attacks) demand a range of capabilities. The balance between community engagement and 'in extremis' response can be found in a doctrine of 'full spectrum policing' supported by 'police operational art.'Too much policing and it is 1776 all over again. Too little policing and the forces of subversion and chaos take over.
See my co-authored papers "Beyond Active Response: An Operational Concept for Police Counterterrorism Response" (with Adam Elkus) at 'New criminologist' and "Postcard from Mumbai: Modern Urban Siege," at 'Small Wars Journal' for more on 'full spectrum policing' and police operational art...
The key is police need to sustain legitimacy in the community...