The De Facto Officer Doctrine is a specific manifestation of a more general principle: not every wrong has a remedy. I think those applying such a principle, however, misapply another important principle: the fact that there is no remedy for an illegitimate action does not make the action legitimate. I would suggest that the DFOD should not be taken to say that the actions of the DFO are in fact legitimate, but rather serves to limit the remedies which would otherwise be available on account of its illegitimacy.
I think the failure to recognize the distinction between the legitimacy of an action, and the availability of a remedy, is behind much of the horrid court precedent that plagues this country. Essentially, the Court takes the position that because prior decisions generally have to be acknowledged as legitimate, the Court must act as though the Constitution and laws have enough nooks and crannies to justify them. The net effect is that the Court makes decisions not based upon the Constitution the Founders wrote, but rather based upon an amorphous fantasy version which continuously adapts itself to fit every decision the Court hands down.
The Constitution is a relatively simple document. If the Court were to recognize that it is neither necessary nor proper to maintain the fiction that every Court decision is legitimately decided, the comparative simplicity of the Constitution would again be revealed. Among other things, when the Bill of Rights uses terms like "unreasonable" or "excessive", such terms are not supposed to be defined primarily in terms of judicial decisions which have held that certain things were appropriate and certain things were not. Rather, they should be applied at face value: if a jury which has examined all the facts surrounding a case would regard a particular punishment as excessive, it is. If a jury which has examined the circumstances surrounding a search would find that it was conducted in unreasonable fashion, or the cop who sought the warrant did not have bona fide probable cause, it should regard the search as illegitimate and not construe against the person who was searched any evidence gained thereby.
If a defendant asks a judge to examine the conduct of an officer in a search, and the judge determines that there is no way an impartial jury would regard the search as "reasonable", it may be appropriate for the judge to suppress the evidence on the grounds that jurors may find it hard to let a guilty person go free if the evidence against him, though illegitimately gathered, appears genuine. On the other hand, it is neither fair nor proper for courts to declare that the the question of whether a search was conducted in "reasonable" fashion should be regarded as having been "settled law" even before the search has took place.
Returning to the DFOD, the right and proper thing for the Court to do would be to acknowledge that the gross misdeeds of various people [including alas many justices themselves] had created a situation where the government has performed many illegitimate actions; allowing such actions to stand would cause unjust harm to some people, but rescinding such actions would cause unjust harm to others. The DFOD is meant to protect the interests of those who would be unjustly harmed by rescinding an apparently-legitimate action should be given priority over those who would be harmed by upholding it. It is not meant to protect the unjust enrichment of those who would benefit from the illegitimate action. The proper resolution is to roll things back in a manner such that (1) those who had a good-faith reliance on the legitimacy of the actions end up about as well off as they would have been without such reliance, and (2) those who would be harmed by the actions are not harmed any more than necessary to achieve (1).
One major problem with trying to apply the DFOD to the present situation is that in general it is designed to ensure that companies have no incentive to leave a phony officer in place. Applying it to the present situation, however, would have the opposite effect. The people who are sheltering the phony officer would be the ones hoping to benefit from his actions; letting them get away with it would encourage more such malfeasance.
The concept of respect for precedent lies at the heart of the rule of law and is a bedrock of a conservative legal philosophy. Respect for precedent is a fundamental safeguard to protect us from the rule of the whims of arbitrary and tryannical judges.
What you are advocating is the abandonment of the rule of law and something even more radical than the "organic" or "living" Constitution doctrine of the liberals.
Your position would invite every far left justice like Ginsburg to abandon all settled law which is inconvenient to the progressive project on the grounds that in her personal opinion she considers it subjectively "illegitimate," unbound by the notion of settled precedent.
In order for there to BE a rule of law and not a rule of the passing whims of radical justices, prior court decisions need to be acknowledged as generally legitimate and the concept of precedent needs to be accorded respect, except in the most egregious instances where an activist court itself has trampled upon precedent and settled law like in Roe v Wade.