The common law rule, accepted at an early date as controlling in this country, was that husband and wife were incompetent as witnesses for or against each other. The rule rested mainly on a desire to foster peace in the family and on a general unwillingness to use testimony of witnesses tempted by strong self-interest to testify falsely. Since a defendant was barred as a witness in his own behalf because of interest, it was quite natural to bar his spouse in view of the prevailing legal fiction that husband and wife were one person. ... The rule yielded to exceptions ... But the Court emphasized that no exception left spouses free to testify for or against each other merely because they so desired.The pressure to break the rule in order to assist prosecutions was already evident, as one justice admitted:
The rule of evidence we are here asked to reexamine has been called a "sentimental relic." ... it was born of two concepts long since rejected: that a criminal defendant was incompetent to testify in his own case, and that, in law, husband and wife were one. ... Any rule that impedes the discovery of truth in a court of law impedes as well the doing of justice. When such a rule is the product of a conceptualism long ago discarded, is universally criticized by scholars, and has been qualified or abandoned in many jurisdictions, it should receive the most careful scrutiny. ... In the present case, however, the Government does not argue that this testimonial privilege should be wholly withdrawn.The privilege was reversed in Trammel v. United States - 445 U.S. 40 (1980):
Held: The Court modifies the Hawkins rule so that the witness-spouse alone has a privilege to refuse to testify adversely; the witness may be neither compelled to testify nor foreclosed from testifying. Here, petitioner's spouse chose to testify against him; that she did so after a grant of immunity and assurances of lenient treatment does not render her testimony involuntary, and thus petitioner's claim of privilege was properly rejected. ...The decision explicitly rejected the view "that the law should not force or encourage testimony which might alienate husband and wife, or further inflame existing domestic differences." Indeed, the case involved a wife who was threatened with prosecution and then offered immunity if she would testify to put her husband in prison.
(a) The modern justification for the privilege against adverse spousal testimony is its perceived role in fostering the harmony and sanctity of the marriage relationship. While this Court, in Hawkins, supra, reaffirmed the vitality of the common law privilege in the federal courts, it made clear that its decision was not meant to "foreclose whatever changes in the rule may eventually be dictated by reason and experience.'" ...
The contemporary justification for affording an accused such a privilege is also unpersuasive. When one spouse is willing to testify against the other in a criminal proceeding -- whatever the motivation -- their relationship is almost certainly in disrepair; there is probably little in the way of marital harmony for the privilege to preserve. In these circumstances, a rule of evidence that permits an accused to prevent adverse spousal testimony seems far more likely to frustrate justice than to foster family peace.
The court's reasoning is unsound. Most marriages never have that kind of stress, where one can only avoid prison by betraying the other. No support is offered for the dubious claim that "there is probably little in the way of marital harmony" when one spouse is willing to testify to avoid prison.
I don't know how many marriages have been destroyed by the abolition of this privilege. Sometimes the destruction is deliberate, as the authorities decide to bust up a couple with a history of domestic violence. Regardless, one of the advantages of traditional marriage has been abolished without significant public debate, by lawyers who believe that the marriage bond is a sentimental relic. When combined with the elimination of other marriage advantages, many younger couples do not see the merits to marriage anymore. The 1980 court reasoned:
As Jeremy Bentham observed more than a century and a half ago, such a privilege goes far beyond making "every man's house his castle," and permits a person to convert his house into "a den of thieves." ... It "secures, to every man, one safe and unquestionable and ever-ready accomplice for every imaginable crime." ...So I guess the court was trying to make some sort of feminist statement, but the privilege had nothing to do with women being regarded as chattel or anything like that. The privilege was available equally to husbands and wives. The better explanation is that the privilege was abolished to undermine the family, and make it easier for prosecutors to pit husbands and wives against each other.
The ancient foundations for so sweeping a privilege have long since disappeared. Nowhere in the common law world -- indeed in any modern society -- is a woman regarded as chattel or demeaned by denial of a separate legal identity and the dignity associated with recognition as a whole human being. Chip by chip, over the years those archaic notions have been cast aside, so that "[n]o longer is the female destined solely for the home and the rearing of the family, and only the male for the marketplace and the world of ideas."