On the whole militarization of the police.
The way I see it the equipment is a symptom of a greater problem of the attitude of how procedures are carried out (warrant service, arrest, ect).
To be blunt, that a cop has a gun on his hip (or slung over his shoulder) is the *least* scary thing about them. In a free society just about anyone can do *that*.
The difference is that Joan Q Public doesn't have police powers. She's got no legal way to break into someone's house, take their stuff, and kidnap the people inside (In other words, serve a warrant, come in with force, take evidence, and put suspects into custody).
It's like how one can propose that cops have "badge cams" when on duty and not want non-police CCW's to have them. Again the difference isn't the gun, but that police are employees of the state who are authorized to use force.
And to go back to the well of Peelian policing. Take a note that all the rules are about how the police interact with the public and the level of force they use, and not the kind of gear they've got.
That isn't to say that the police buying (or being granted) lots of equipment that they can't afford to keep, that eats a budget that could have been spent on training or other more useful stuff, isn't a problem. The use it or loose it dictum does come into play. But again, it's symptomatic of a larger problem.
As for which police gear is kosher, I'd say put it on parity of what the public can own. As the police are civilian, and that'd be a simple enough rule of thumb.