They don't have an underclass of criminals who will continually breed further underlings. Until people realize that this underclass exists, and there is little (if anything) that we can do about it then crime will remain a problem in this country.
We can't copy another countries justice system because the people within the two countries are very different.
I think it's a bit of a slippery slope with condemning whole bits of the country, the death penalty isn't a solution to that.
There is nothing stopping us having the Nordic system apart from our obsession with using Prison as a panacea, over using custodial solutions and putting not much effort into making people different in the first place. Prison doesn't 'work' because it can't fix where people came from, the people they hang out with, the culture they are into and the circumstances they return to. The Nordic and Canadian principles are built around appropriate custody and proper interventions, ours are built on big warehouses that people scream about if someone in them gets to watch a TV for good behaviour.