The more I think about the (purely judge-made and policy-driven) doctrine of prosecutorial immunity, the less I like it. The underlying idea is that making prosecutors vulnerable to lawsuits for cheating in the courtroom would make them less vigorous prosecutors. Of course, when they’re cheating, reduced vigor is exactly what you want. But when they’re not, the concern is that they might pull their punches for fear of future liability.
But there’s a simple fix for that concern: as the Federal government substitutes itself as the defendant when a federal official is sued for official actions, the county or the state that employs the prosecutor can substitute itself as the defendant in prosecutorial-misconduct cases. Of course, it could choose not to, either in general or on a case-by-case basis. But why should the courts interfere as between the prosecutor and his employer? And in any case, why should the victim of a frame-up lose, not only his chance of recovery, but his day in court?
The notion that the enormous power of prosecution to wreck someone’s life ought to be wielded in completely unreviewable fashion simply doesn’t fit our basic notions of justice.