I find it hard to believe that an individual officer in a situation where they are scared chooses to escalate on the basis of how the DA looks. It's more likely that the situation triggers an emotional reaction which they're unable to process at the time, and because they're unable to remove themselves from the situation they cease to act rationally.
Human beings will ultimately act like human beings in these situations. It's very easy to expect something else when you're not the human being under threat.
The only way to prevent human beings from acting in the default way human beings act is rigorous evidence-based training. No proposition that there must have been something else they could have done is meaningful unless it's backed up by specific, rigorous, evidence-based training for the situation in question.
Absent that, we're asking people to respond to threats unrealistically. We're making them sick and commanding them to be well.
It's more that they know they will, with near certainty, never be held accountable for improper use of force, so there's no reason not to immediately escalate the situation.
