We don't need to excuse unwarranted police violence as a society, but it's equally unfair to outsource dealing with violent and dangerous situations to others and then glibly remove any means they have to deal with those situations without getting killed themselves.
I think you and jessaustin may be using different interpretations of that term, judging by their reference of the McDonald shooting. People are much more ok with police officers doing what they need to do to keep themselves and others safe at the time (your usage) than they are with officers lying about why they used deadly force after the fact to keep from getting in trouble (their usage).
McDonald is the reason I'd like the "firearm" breakout, because "deadly weapon", "no firearm", and "no attack in progress" describes a somewhat common class of police fatalities that are probably mostly unjustified.