recidivism and deterrence in general are not the same thing. high recidivism does not mean that people who haven't been imprisoned yet aren't deterred from committing crimes.
It's a multi-variable system. It could be that other conditions and effects override what is, in other circumstances, a solid deterrent.
Threat of long imprisonment works great on the guy who doesn't want to lose his cushy job and easy life. It doesn't work as well on someone with nothing and no hope of gaining anything.
Saying it doesn't serve as a deterrent for a certain class of individual is a fair statement, saying it doesn't work, full-stop is most certainly wrong.
is this actually true? as I understand it, we are well past the peak of criminal activity ( at least in the US).