This Rule governs the disclosure by a lawyer of information relating to the representation of a client during the lawyer's representation of the client. ... A fundamental principle in the client-lawyer relationship is that, in the absence of the client's informed consent, the lawyer must not reveal information relating to the representation.The constitutional basis is the Sixth Amendment:
In all criminal prosecutions, the accused shall enjoy the right to a speedy and public trial, by an impartial jury of the State and district wherein the crime shall have been committed, which district shall have been previously ascertained by law, and to be informed of the nature and cause of the accusation; to be confronted with the witnesses against him; to have compulsory process for obtaining witnesses in his favor, and to have the Assistance of Counsel for his defence.The thinking is that "Assistance of Counsel" requires because able to ask your lawyer confidential questions about your predicament without that being used against you in court.
Here is the lawsuit against Rule 1.6, with further argument here and here.
I am sorry, but this stuff is incoherent and is going nowhere. Apparently some guy is mad that he cannot get copies of the communications between his wife and her lawyer in a divorce court battle. There is no explanation why those documents would be useful or relevant, and no explanation of how the legal profession would ever function without an attorney-client. I realize that the privilege is occasionally abused, but this guy gives no evidence of any abuse.