In Ferri v. Ackerman, the U.S. Supreme Court ruled that a court-appointed attorney cannot be sued for malpractice by his or her client in relation to services performed as part of their official duties. The case arose when Joseph P. Ferri, who was convicted of mail fraud and other crimes, attempted to sue his former lawyer John H. Ackerman III for negligence and breach of contract after losing an appeal against his conviction due to what he claimed were errors made by Ackerman during trial preparation and presentation before the jury. The Supreme Court held that public defenders are immune from such lawsuits because they function as officers of the court while carrying out their responsibilities related to representing clients in criminal cases; thus they should enjoy similar protections afforded judges and prosecutors who also can't be sued over actions taken within scope of their professional roles. This decision underscored how important it is for public defenders - like all attorneys - to provide competent representation but acknowledged that holding them liable in civil suits could deter qualified lawyers from serving in this capacity given potential personal financial risks involved.

In the dissenting opinion for Ferri v. Ackerman, Justice William Rehnquist argued that court-appointed attorneys should not be immune from malpractice lawsuits brought by their clients. He contended that such immunity would undermine the legal profession's responsibility to provide competent representation and could potentially lead to a decline in professional standards. Furthermore, he believed it was unjust for private attorneys to face potential liability while public defenders were shielded from similar consequences for their actions. In his view, this discrepancy created an unfair system where some lawyers were held accountable for their mistakes while others were not.