People tend to behave if they know they are being watched. Yeah it's not going to stop crime 100%, but I bet you it will (and it has) help reduce crime by double digit percentages.

Look at places where there are CCTV cameras all over, there is very little crime there compared to the United States. I won't use China as an example because then you are going to attack me for saying it's an authoritarian state. In that case I will use democratic examples: Taiwan, South Korea, Singapore.