Why does the claim that a police presence is needed somewhere result in the death of innocent people? Why are the police prepared for war when visiting someone

Why does the claim that a police presence is needed somewhere result in the death of innocent people? Why are the police prepared for war when visiting someone's residence? What situation, time and time again, can possibly justify this kind of repeated response? Put in another, more unpleasant way, how many innocent deaths are worth one police officer death, because law enforcement justifies this due to (truly existent, but I think extremely overstated) danger inherent in the job. But I think any rational mind can perceive it's way too far skewed in one direction.