Right, also how does crime prevention make sense? I mean someone is innocent until he commits crime right? So it would mean arresting innocent people because "they were going to commit a crime".

This is a slippery slope, I can see it being abused real quick. So I tend to think that police isn’t meant to directly prevent me from getting killed. Police is meant for arresting the culprits, and that would indirectly prevent me from getting killed because it’s not worth the risk.