Problem is the cameras do not prevent crime, they only help track down the culprit.. and not always too well.
I for one would not want to give up my privacy for something that “might” work or “might” catch a bad guy, but will do nothing to stop it.
Having firefighters doesn't prevent fires either...but I'm damn glad they're there. No, the cameras may not prevent crime but if they help, in any way, in catching the perps then I'm glad they're there too.
As another poster stated, you have no right to expect privacy on public streets and sidewalks.