Actually, you can pretty much drop the deterrence part of that statement. In most cases, there is precious little the police can (or will) do prior to the actual commission of a crime. And in far too many instances there seems to be evidence that even during the commission of a crime they will wait until after the criminals have left, then make a show of "investigating" the crime.
For sure, I wouldn't want to put my life on the line as the police do, especially for the pitiful pay they generally make. And in many of the cases there are judicial bars to them actually doing anything constructive before the crime. And now it's gotten to the point where, when they do catch a criminal, they have to treat him or her with kid gloves or risk a lawsuit and horrific publicity.
It's just not worth it! People had better be prepared to defend themselves and their own.