What always confuses me (I live in a country where the police don't generally get guns, even) is what they're preparing for with this sort of thing? A full-on war? Like, if they need hundreds of assault rifles for police work, then arguably society has already collapsed and the police are probably surplus to requirements anyway.
The rifles used by everyday police are the same as those owned by tens of millions of civilians. These weapons are cosmetically similar to those used by the military, but they have the same functionality and fire the same cartridge as the Ruger Mini-14.[1] They are semi-automatic. Every "bang!" requires a pull of the trigger. The reasons police have these weapons are because pistols are less accurate, have shorter range, and are unable to penetrate body armor. These rifles are usually locked in the back of the vehicle and only brought out for standoff situations, or if the cop has retreated due to being outgunned. Such occasions are rare, but when they happen, those rifles are worth their weight in gold (as are the fire extinguishers and medical kits in practically all police cars).
Moreover, police have always used the latest weaponry. A century ago, they were equipped with the Thompson submachine gun[2] and the Browning Automatic Rifle[3] (both of which are fully automatic weapons).
I agree that police have gotten more militarized over time, and I would love to roll that back, but it's also true that many of those arguing in this thread are either misled or disingenuous. We're much more likely to convince others if we make sure our arguments and our facts are unimpeachable.
1. https://commons.wikimedia.org/wiki/File:Ruger_Mini-14.jpg
2. https://commons.wikimedia.org/wiki/File:Thompsonad1sm.jpg
3. https://commons.wikimedia.org/wiki/File:Firearms_practice,_1...
