Look, we live in a day and age when too many don't want to take responsibility for anything. It's always someone elses fault, and we all suffer from this lack of willingness to stand up and say "yes, I did that. Because it seemed like the right thing to do." Some call this a lack of "common sense". Cops are in the middle of it just like the rest of us, they suffer from it too - maybe more so: That's the way it is.
How *should* it be? Look no further than this thread. Why is this DA's refusal to prosecute such a newsworthy item? Because it happens so rarely. More power to this guy. If the people who work in the system (like the cops) start to the get the idea that the folks higher up on the ladder (like this DA) are starting to exercise judgement and common sense, then they'll start to do the same. The concept is pretty simple, really. It's called leadership.