Activist Danna Miller Pyke protests near the Dallas site where the ExxonMobil annual shareholder meeting is taking place in May. (Jae S. Lee/The Dallas Morning News via Associated Press)

Robert Post is the dean and a professor of law at Yale Law School.

Global warming is perhaps the single most significant threat facing the future of humanity on this planet. It is likely to wreak havoc on the economy, including, most especially, on the stocks of companies that sell hydrocarbon energy products. If large oil companies have deliberately misinformed investors about their knowledge of global warming, they may have committed serious commercial fraud.

A potentially analogous instance of fraud occurred when tobacco companies were found to have deliberately misled their customers about the dangers of smoking. The safety of nicotine was at the time fiercely debated, just as the threat of global warming is now vigorously contested. Because tobacco companies were found to have known about the risks of smoking, even as they sought to convince their customers otherwise, they were held liable for fraud. Despite the efforts of tobacco companies to invoke First Amendment protections for their contributions to public debate, the U.S. Court of Appeals for the D.C. Circuit found: “Of course it is well settled that the First Amendment does not protect fraud.”

The point is a simple one. If large corporations were free to mislead deliberately the consuming public, we would live in a jungle rather than in an orderly and stable market.

ExxonMobil and its supporters are now eliding the essential difference between fraud and public debate. Raising the revered flag of the First Amendment, they loudly object to investigations recently announced by attorneys general of several states into whether ExxonMobil has publicly misrepresented what it knew about global warming.

The National Review has accused the attorneys general of “trampling the First Amendment.” Post columnist George F. Will has written that the investigations illustrate the “authoritarianism” implicit in progressivism, which seeks “to criminalize debate about science.” And Hans A. von Spakovsky, speaking for the Heritage Foundation, compared the attorneys general to the Spanish Inquisition.

Despite their vitriol, these denunciations are wide of the mark. If your pharmacist sells you patent medicine on the basis of his “scientific theory” that it will cure your cancer, the government does not act like the Spanish Inquisition when it holds the pharmacist accountable for fraud.

The obvious point, which remarkably bears repeating, is that there are circumstances when scientific theories must remain open and subject to challenge, and there are circumstances when the government must act to protect the integrity of the market, even if it requires determining the truth or falsity of those theories. Public debate must be protected, but fraud must also be suppressed. Fraud is especially egregious because it is committed when a seller does not himself believe the hokum he foists on an unwitting public.

One would think conservative intellectuals would be the first to recognize the necessity of prohibiting fraud so as to ensure the integrity of otherwise free markets. Prohibitions on fraud go back to Roman times; no sane market could exist without them.

It may be that after investigation the attorneys general do not find evidence that ExxonMobil has committed fraud. I do not prejudge the question. The investigation is now entering its discovery phase, which means it is gathering evidence to determine whether fraud has actually been committed.

Nevertheless, ExxonMobil and its defenders are already objecting to the subpoena by the attorneys general, on the grounds that it “amounts to an impermissible content-based restriction on speech” because its effect is to “deter ExxonMobil from participating in the public debate over climate change now and in the future.” It is hard to exaggerate the brazen audacity of this argument.

If ExxonMobil has committed fraud, its speech would not merit First Amendment protection. But the company nevertheless invokes the First Amendment to suppress a subpoena designed to produce the information necessary to determine whether ExxonMobil has committed fraud. It thus seeks to foreclose the very process by which our legal system acquires the evidence necessary to determine whether fraud has been committed. In effect, the company seeks to use the First Amendment to prevent any informed lawsuit for fraud.

But if the First Amendment does not prevent lawsuits for fraud, it does not prevent subpoenas designed to provide evidence necessary to establish fraud. That is why when a libel plaintiff sought to inquire into the editorial processes of CBS News and CBS raised First Amendment objections analogous to those of ExxonMobil, the Supreme Court in the 1979 case Herbert v. Lando unequivocally held that the Constitution does not preclude ordinary discovery of information relevant to a lawsuit, even with respect to a defendant news organization.

The attorneys general are not private plaintiffs. They represent governments, and the Supreme Court has always and rightfully been extremely reluctant to question the good faith of prosecutors when they seek to acquire information necessary to pursue their official obligations. If every prosecutorial request for information could be transformed into a constitutional attack on a defendant’s point of view, law enforcement in this country would grind to a halt. Imagine the consequences in prosecutions against terrorists, who explicitly seek to advance a political ideology.

It is grossly irresponsible to invoke the First Amendment in such contexts. But we are witnessing an increasing tendency to use the First Amendment to unravel ordinary business regulations. This is heartbreaking at a time when we need a strong First Amendment for more important democratic purposes than using a constitutional noose to strangle basic economic regulation.