Ohwilleke has mentioned a couple of times on this SE that prosecutorial discretion is almost absolute in the USA. So how has this been defended in law and what are some laws/cases that have made that the case?
I'm assuming that, as the prosecutor is a political appointee, his discretion is still limited to what can keep him elected. His choices can still be disciplined by being voted out of office, so he cannot do entirely whatever he wants.
I don't know what normative justifications underpin the principle in U.S. law, but I present this as a comparative look at how the same principle is justified in Canada.
The Supreme Court of Canada has said the justification for non-interference with prosecutorial discretion is separation of powers, rule of law, and institutional competence.
In R. v. Power, [1994] 1 SCR 601, the Court quoted from several sources with approval:
In Canada, it is the executive which assumes primary responsibility for administering the criminal law, as was held by a majority of the Supreme Court in Skogman v. The Queen. This stems from the fact that there must be an authority which decides whether the judicial process should be set in motion and what form the prosecution will take. Decisions concerning the operation of criminal justice involve important considerations relating to the public interest. From this perspective, the actions of the Attorney General are hybrid in that there is a perpetual moving to and fro between his legal and political functions. That is why the Attorney General must answer politically to Parliament for the manner in which the Crown exercises its powers.
...
It is fundamental to our system of justice that criminal proceedings be conducted in public before an independent and impartial tribunal. If the court is to review the prosecutor's exercise of his discretion the court becomes a supervising prosecutor. It ceases to be an independent tribunal.
And more recently, in R. v. Nixon, 2011 SCC, at para 20:
the independence of the office [is] “a constitutional principle in this country”
And in Krieger v. Law Society of Alberta, 2002 SCC 65:
The quasi-judicial function of the Attorney General cannot be subjected to interference from parties who are not as competent to consider the various factors involved in making a decision to prosecute. To subject such decisions to political interference, or to judicial supervision, could erode the integrity of our system of prosecution. Clearly drawn constitutional lines are necessary in areas subject to such grave potential conflict.
It is defended as anything else is strictly unworkable. There is plenty of legal doctrine here, but think about it, the system would stop if prosecutors had to prosecute everything before them no matter what.
