Even in an adversarial system, the point of prosecutors is not to be "as vicious as the law allows them to be". The point is to pursue actual crime as vigorously as they can. Instead, we are seeing repeated instances of prosecutorial misconduct where the prosecutor's office tries to win the case on a legal technicality, even when it's actually counter to the basic goal of justice (i.e. establishing the truth of charges) - by, for example, trying to place procedural hurdles in the way of procedures, like DNA tests, that might exonerate the defendant, or withholding evidence that might indicate innocence, but which the prosecutor is not legally obligated to introduce. Here's a recent example:

https://www.washingtonpost.com/news/the-watch/wp/2017/09/25/...

There's absolutely no social good coming out of such behavior, and it should be pointed out and castigated.

And yes, this does, in fact, happen, because prosecutors are effectively rewarded for successful prosecutions, regardless of the false positive rate.