In my mind, police officers sign up for a dangerous job knowingly - that's why they're revered as heroic by many in society. They are willing to put themselves at risk to protect society from harm, and that's noble.
What most police academies teach is the opposite. They teach officers to put their own safety over that of everyone else. They talk in terms of "reducing officer casualties" and "overwhelming force". This is not a heroic police officer sacrificing himself for society; it's jackbooted thugs threatening, terrorizing and killing the very civilians they are supposed to protect. Turns out it's really hard to tell a bad guy from a good guy by looking at them, so they play it safe and treat everyone like a bad guy.
Not every officer thinks this way, but it's common enough that it leads to a lot of police shootings. IMO a police officer should be more willing to take a bullet than put one into someone. I realize body armor isn't foolproof, but the job is inherently dangerous and the officer goes into it knowing that - something a person on the street doesn't get.