I'm not blaming prosecutors, or pretending that Canada doesn't have problems. Rather, I'm asking questions because I don't understand the nuts and bolts of the US justice system.
Consider elected District Attorneys. In Canada, Crown Prosecutors are appointed and the position is meant to avoid becoming political. That doesn't always happen, since becoming a CP is often a route to either become a judge (our judges are also appointed), or a politician, but I digress.
As another example, under Canadian law, if you're charged with a crime, it starts with the police office involved 'laying an information'. Basically, the police officer will draft a sworn summary of the case and present it to a Justice of the Peace. Then, the JP decides whether there is enough evidence to actually go forward. We don't have the concept of a grand jury, nor do Crown Prosecutors necessarily have to be involved before a charge is formally brought upon the defendant.
As for paranoid suburbanites, we have more than our share, and for good reason. Some of our laws (ie - our Young Offenders Act) admittedly leave a little to be desired and some awfully bad people get to walk the streets. For example, my city has a number of extremely violent sex offenders (who the parole board has ruled at an extremely high risk to re-offend) walking around free. Ask me how I feel about my Mom getting into her car alone at night....
Despite sharing a border and coming from the same legal tradition, our criminal systems are dramatically different. Consequently, I can't really comment on the American system because I don't understand it well enough to know where concepts like discretion come from and who has the right to demonstrate discretion.