It's rare when a crime is committed in the presence of a police officer, but it's always committed in the presence of its victims. Police frequently respond to crimes only AFTER they have happened, AFTER the citizen has been victimized, AFTER victims have been shot. That is not a knock on cops, it just is what it is.
This introduces a really serious question: who IS responsible for our safety when the police are not there? When someone comes to break into our homes, who do we turn to for help? When someone pulls a gun and attempts to rob us while we are walking down the street, what do we do? When some nut decides to walk into a crowded establishment bent on as much murder and mayhem as possible, how do we protect ourselves? The answer has profound implications for a free society.
It's ridiculous to suggest that we leave our fate in those circumstances to chance, hoping some lunatic--religiously motivated or just plain crazy--will choose not to harm us or our loved ones. It's equally ridiculous to leave the fate of our families, homes, and community in those situations to law enforcement when it admits that it “cannot be everywhere at once.” Who, then, fills the void? Us? Our neighbors? Something else?