Even from a security point of view, that's only true if they actually use it effectively. From direct personal experience, this is not always the case: just because a camera is there, that doesn't necessarily mean anyone will bother to check it, even following the theft of a considerable sum of money.
I suppose in theory, if you blanketed the entire country with CCTV (just one town is no good, the crime can move to the next town over) then you might have a deterrent effect, but of course all the other concerns about mass surveillance would still apply.
Yes, but it won't happen. It is stupidly expensive and if you leave mild criminals nowhere to go they will destroy the CCTVs (happens a lot with speed cameras, and that's just normal angry drivers).
I suppose in theory, if you blanketed the entire country with CCTV (just one town is no good, the crime can move to the next town over) then you might have a deterrent effect, but of course all the other concerns about mass surveillance would still apply.