Hey, these guys need something to relieve the boredom of patrol duty, don't they?
But seriously, judging from all the quasi-military hardware some police departments have amassed, you'd think they're gearing up to fight a land war against some pipsqueak nation. Even in cities like L.A. with rampant gang activity, I can't see how a lot of this stuff is even remotely appropriate to the task. But at least the L.A.P.D. can spread the costs across a fairly large tax base. That's not the case with a number of medium-sized cities that have also gone for this sort of thing.
If the late Dwight D. Eisenhower had become a big-city mayor rather than president, I suspect that he would have had a problem with this sort of thing.