Legally speaking it most certainly is, otherwise cops, soldiers, or criminals killing would be treated the same way. Morally... perhaps it's a grey area but one thing I'm sure you agree with is that there is a massive difference between a military conflict between armed parties, and a conflict between police and anything from unarmed bystanders to criminals. There's a common sense principle of proportionality that hasn't been observed in too long.
Jack the Ripper wasn't a surgeon because "cutting is really no different anywhere in the world".
I guess that depends doesn't it. A gunfight between armed gangsters and cops in the middle of an urban area isn't all that different than a small american patrol in an urban area in say Iraq, Libya or Syria getting into a gun fight with a group of insurgents. In both cases there will be innocent bystanders likely caught in the middle. As far as both a logical and moral perspective goes, American soldiers have far less right to be killing people in those countries than a police officer defending against armed criminals in their own jurisdiction.
All these arguments on it being 'right' are based on the assumption that America's armies currently being used to invade other nations is 'right'. If America's armies weren't being used to oppress and and control other nations, I'd maybe agree with you more.
This is exactly how I'd frame any situation to defend any argument or position no matter how inappropriate it is.
Dressing up police like soldiers and letting them rip on harmless and unarmed people is most definitely not the same as soldiers in a declared conflict making collateral damage while fighting a genuinely dangerous army armed to the teeth. Soldiers dress like soldiers because they have to go fight other soldiers and face machine gun or sniper fire, mortars, IEDs, grenades, tanks, etc. Police dresses up like soldiers to fight some people with a bandanna and a passive aggressive sign. Are you telling me that's the same?
Unless a country declares war on its citizens the police should not be allowed under any circumstances to treat them as an enemy combatant. And it doesn't even matter really, the fact that the US Army is more that willing to commit war crimes should have no impact on what the Police does to its citizens.
This is what happens when common sense stops being common, when people no longer understand "appropriate force" and "proportionality".
US citizens deserve the same response in daily life from a police under the "serve and protect" banner that an enemy combatant gets from the opposing military during an active conflict? You can't treat every citizen as if they are the worst possible one. If you got this "you could be the worst ever" treatment in any other situation you would certainly not find acceptable to reference the fact that the army also does it while in a war.