Police probably shouldn't ever fire their weapons first...
Of course that would make being an officer slightly more physically dangerous, but only slightly. Most never have cause to fire their weapons in the line of duty anyway.
Some areas of the USA are actually very dangerous. In these areas there is a much higher likelihood of suspects being harmed and dangerous.
You’re basically asking other humans to implement a sound system (where false negatives mean they die) in an area with relatively high event rates. This doesn’t give me any moral clarity.
In cushy neighborhoods sure police officers likely do implement a complete system and no one gets shot. That’s much easier to justify based on basic probabilities.
This study finds a substantial difference in high crime areas, but still most officers never discharge their weapon in the line of duty:
http://www.pewresearch.org/fact-tank/2017/02/08/a-closer-loo...
About one-in-five officers (22%) in areas with at least six and but fewer than 10 violent crimes per 1,000 residents in 2015 have ever fired their service weapon. By contrast, about a third (32%) of officers who work in areas with a lower violent crime rate have discharged their gun. In areas where the violent crime rate is 10 or more, 28% of officers have fired their weapon. However, that proportion is not significantly different from the share that works in communities with fewer than six or six to fewer than 10 violent crimes per 1,000 residents.
Maybe the best way to stop them firing first is to not let them carry a firearm.
We can look at this this on a national level where we're already in pretty bad shape with a murder rate of 4.9 [1] compared to less than 1 for most of Europe. But where things get really insane is when you start breaking it down to where these events are often happening. Crime, especially violent crime, in the US is very centralized into a number of relatively small areas. For instance these [2] are the crime data for Ferguson, Missouri where Michael Brown was killed. In the year Michael Brown was killed, their homicide rate was double the US average. It's now skyrocketed to 42.8. To give some context to that 42.8 the murder rate in Mexico is 16.35. In Columbia it's 26.5. There are actually only 5 nations with a murder rate higher than Ferguson. And you'll find that these extreme rates of violence tend correlate pretty well to areas where the reported police violence is also coming from.
So the point here is that comparing how the police function in countries with little to no reason to expect extremely dangerous scenarios (or outcomes) to countries where such expectations are perfectly justified is not really logical. Here's an interesting thought experiment. Swap the police force of [less dangerous nation] with the police force of the US. Would you expect the behavior of the US police force in the now much more safe nation to change? What of the police from the safer nation now placed in a nation where people randomly killing police is actually a thing?
[1] - https://en.wikipedia.org/wiki/List_of_countries_by_intention...
[2] - http://www.city-data.com/crime/crime-Ferguson-Missouri.html
Did you notice how the officer was constantly tucking himself around the corner? He had no way of knowing whether there were more individuals waiting to ambush the officers. And that is a perfectly justifiable fear given the context of this situation. And the victim in this case reached behind his back multiple times, even after being told precisely not to. He could have been reaching for a weapon or it could have been something for more dangerous - imagine he was reaching for a detonator. It's easy to condemn the police officer, but at the same time this shooting took multiple unbelievably provocative actions on part of the victim to reach this point: point rifle outside hotel room apparently in vicinity of other hotel guests, decide to reach around back when specifically told to keep hands visible, repeat that mistake and reach even more directly towards your waist. I obviously can't condone the act, but on the other hand I also can't entirely condemn it either. It's an extremely unfortunate scenario.
[1] - https://www.youtube.com/watch?v=DqLd-lEFqsM