A reasonable observer might ask: "If stolen documents can't be used in a court of law, why can journalists use them to write about Ashley Madison customers?"
I'm a journalist, not a lawyer, but I'm pretty sure I can provide a law-based answer to that question by raising two points:
(1) A 2001 U.S. Supreme Court (SCOTUS) case gave journalists the right to report on information they receive that has been illegally obtained;
(2) Evidence provided in a courtroom, and evidence required in a newsroom are two very different things.
The SCOTUS case is Bartnicki v. Vopper, 532 U.S. 514 (2001), which involved a radio commentator who played a tape on his public-affairs show of an intercepted conversation between two union officials during contentious collective-bargaining negotiations for teachers at a Pennsylvania High School. An unknown person had intercepted and recorded the call, and the tape wound up being played on another radio station, and local newspapers published its contents.
Here is how Justice John Paul Stevens described the issues at hand:
These cases raise an important question concerning what degree of protection, if any, the First Amendment provides to speech that discloses the contents of an illegally intercepted communication. That question is both novel and narrow. Despite the fact that federal law has prohibited such disclosures since 1934, this is the first time that we have confronted such an issue.
The suit at hand involves the repeated intentional disclosure of an illegally intercepted cellular telephone conversation about a public issue. The persons who made the disclosures did not participate in the interception, but they did know—or at least had reason to know—that the interception . . . was unlawful. Accordingly, these cases present a conflict between interests of the highest order—on the one hand, the interest in the full and free dissemination of information concerning public issues, and, on the other hand, the interest in individual privacy and, more specifically, in fostering private speech. The Framers of the First Amendment surely did not foresee the advances in science that produced the conversation, the interception, or the conflict that gave rise to this action. It is therefore not surprising that Circuit judges, as well as the Members of this Court, have come to differing conclusions about the First Amendment's application to this issue. Nevertheless, having considered the interests at stake, we are firmly convinced that the disclosures made by respondents in this suit are protected by the First Amendment.
Putting it more succinctly, Stevens wrote:
Simply put, the issue here is this: "Where the punished publisher of information has obtained the information in question in a manner lawful in itself but from a source who has obtained it unlawfully, may the government punish the ensuing publication of that information based on the defect in a chain?" Boehner, 191 F. 3d, at 484-485 (Sentelle, J., dissenting).
How did the court approach the First Amendment issues before it? Again, Justice Stevens provides the framework;
First, respondents (the journalists) played no part in the illegal interception. Rather, they found out about the interception only after it occurred, and in fact never learned the identity of the person or persons who made the interception. Second, their access to the information on the tapes was obtained lawfully, even though the information itself was intercepted unlawfully by someone else. . . . Third, the subject matter of the conversation was a matter of public concern.
The court's ultimate ruling, siding with a free press over privacy concerns, rode largely on the shoulders of truth. From Justice Stevens:
As a general matter, "state action to punish the publication of truthful information seldom can satisfy constitutional standards." Smith v. Daily Mail Publishing Co., 443 U. S. 97, 102 (1979). More specifically, this Court has repeatedly . . . held that "if a newspaper lawfully obtains truthful information about a matter of public significance then state officials may not constitutionally punish publication of the information, absent a need . . . of the highest order." Id., at 103; see also Florida Star v. B. J. F., 491 U. S. 524 (1989); Landmark Communications, Inc. v. Virginia, 435 U. S. 829 (1978).
In the end, this was a classic battle between privacy and free speech--and privacy lost. Wrote Stevens:
In these cases, privacy concerns give way when balanced against the interest in publishing matters of public importance. As Warren and Brandeis stated in their classic law review article: "The right of privacy does not prohibit any publication of matter which is of public or general interest."
As for item No. 2 above, it touches on the Rules of Evidence, which I suspect many law students would say are a major pain in the posterior to learn. I don't have a formal legal education, but I've been involved in more court cases than I care to count, so I think I can make an educated guess about why courts view evidence allowed in court very differently from information published in the press.
My understanding is that a lawyer generally has to "lay a foundation" before evidence can be accepted in a court case. For example, consider a possible civil case over alleged insurance fraud. A plaintiff's lawyer in such a case likely would want to enter all sorts of documents to show that his client was defrauded. But how could he show the documents were legitimate? One way might be to put his client on the stand and have her testify that these were documents the insurer sent her and she kept them in a file cabinet at home. More than likely, that would lay the foundation for showing the documents were real and could be entered as evidence.
That process becomes difficult when the evidence has allegedly been stolen. Who is going to testify to the documents' authenticity? Is the thief going to do that? Not likely. I suspect that's why U.S. Judge Ross in Missouri excluded the stolen Ashley Madison data. There is no way to lay a foundation that the information is authentic.
On the other hand, Ross found that the data likely could be entered if produced as part of the discovery process. I'm guessing that's because someone, likely an Ashley Madison official, will be able to lay the necessary foundation for use as evidence.
I suspect some readers will respond to this explanation with: "Well, that's all well and good, but it's still unfair." I can't say that's an unreasonable statement. But the law has found that lawyers and journalists, while both have serious rights and responsibilities, operate in different arenas when it comes to the evidence they need to do their jobs.