This is not unavoidable, but a specific aspect of America's incarnation of the adversarial system. In plenty of other jurisdictions, prosecutors have a more neu

This is not unavoidable, but a specific aspect of America's incarnation of the adversarial system. In plenty of other jurisdictions, prosecutors have a more neutral, quasi-judicial role, where – especially during the investigative phase of a case – they are required to act more like French examining magistrates. In some jurisdictions, prosecutors can even have an affirmative duty to act on the behalf of the defendant if they believe that the defendant is not receiving a fair trial. There are also pragmatic issues; prosecutorial accountability matters even in adversarial systems (accountability not in the sense of dealing with prosecutorial misconduct, but to ensure that prosecutors act consistently and in the public interest). Prosecutors aren't or shouldn't be free agents.