Police sometimes face mortal threats. They also face innocent people whom they mistakenly judge to pose a mortal threat. If too slow to react to the former, the police risk being killed. If too quick to react to the latter, they risk killing innocent civilians. What is the right way to balance these risks? Three options present themselves:
(1) Give some extra weight to protecting innocent civilians, as per the duty to "protect and serve".
(2) Give some extra weight to their own life, as per the standard prerogatives of self-interest. OR
(3) Count both risks equally, and so seek to minimize innocent deaths (whether self or other) overall.
Though the choice between these options might make a slight difference at the margins, the amount of "extra" weight that could be justified in either of the first two options is presumably limited in size. So I take it that police should give close to equal weight to either type of risk. They should not, for example, kill someone who is very likely to be innocent.
While an extremely rough estimate, this analysis suggests that the vast majority of police shootings are "tragic mistakes" rather than objectively justified responses to genuine mortal threats. If police are making approx 450 "tragic mistakes" annually, while losing only 30 of their own number, this would seem to suggest a terrible miscalibration: the burden of risk is falling overwhelmingly upon the civilian populace, instead of being fairly shared between civilians and police alike.
I think that last sentence is mistaken, though. To see why, suppose that police were practically invincible: that attempts on their lives would almost invariably fail. In that case, shooting someone 49% likely to be innocent would clearly not value police and civilian lives equally. They could wait to be more certain of the threat, thereby reducing the risk to innocent civilians, without facing any significant increase in risk themselves. Of course, in reality the police are not so invincible. But Coons' model does assume that they are much more likely to emerge victorious from a gun fight. (Otherwise the estimated number of mortal threats would be much lower, and the number of "tragic mistakes" correspondingly higher.) So a moderated version of the same principle would seem to apply: police could decrease the risk to innocent civilians by more than the increase in risk to themselves, by adopting a standard that is more stringent than merely requiring a "probable" threat.
One complication that isn't addressed here: The division between "mortal threats" and "innocent civilians" is a false dichotomy. Police may often face aggressive criminals who aren't truly innocent, but neither do they pose a genuine mortal threat to armoured police officers. While mere criminality doesn't mean that you deserve to die(!), one might nonetheless judge it reasonable for this population to bear a (significantly) greater share of the risk burden. Anyone inclined towards that view would likely want to reserve the term "tragic mistake" for truly innocent victims, and use a more neutral label such as "unnecessary killings" for the broader category that Coons is talking about. And we'd then need to know how many of these unnecessary killings had innocent vs criminal victims. If overwhelmingly the latter, some might on that basis decide that the status quo was not so obviously unjust after all. It'd take different arguments from those surveyed here to argue against such a position.