Tuesday’s Supreme Court decision in Jennings v. Rodriguez was widely viewed as an anticlimax. The case involves a group of immigrants being held in custody without any hope of bail. They argue that their indefinite detention violates due process, but the majority declined to resolve the constitutional question, sending the case back down to the lower court. In a sense, the plaintiffs are back where they started.

Justice Stephen Breyer, however, saw something far more chilling in the majority’s opinion. Taking the rare and dramatic step of reading his dissent from the bench, Breyer cautioned that the court’s conservative majority may be willing to strip immigrants of personhood in a manner that harkens back to Dred Scott. The justice used his impassioned dissent to sound an alarm. We ignore him at our own peril.

Jennings involves three groups of noncitizen plaintiffs: asylum-seekers, immigrants who have committed crimes but finished serving their sentences, and immigrants who believe they’re entitled to enter the country for reasons unrelated to persecution. A high percentage of these types of immigrants ultimately win the right to enter the U.S. But federal law authorizes the government to detain them while it adjudicates their claims in case it secures the authority to deport them instead.

The detention of these immigrants—often in brutal facilities that impose inhuman punishments—has, in practice, dragged on for months, even years. There is no clear recourse for detained immigrants who remain locked up without a hearing. In 2001’s Zadvydas v. Davis, the court found that a similar scheme applied to “deportable aliens” would almost certainly violate the Fifth Amendment’s Due Process Clause. To avoid this constitutional problem, the court construed the law as limiting detention to six months.

But in Jennings, the court’s five-member conservative majority interpreted another federal law to permit indefinite detention of thousands of aliens, with no apparent concern for the constitutional problems that reading creates. Justice Samuel Alito, writing for the majority, revealed from the outset of his opinion that he dislikes Zadvydas, dismissing it as a “notably generous” holding that avoided the constitutional issue in order to secure due process for immigrants. Unlike the Zadvydas court, Alito has no interest in protecting the constitutional rights of noncitizens. Instead, he read the current statute as stingily as possible, concluding that it did, indeed, allow the government to detain all three groups of immigrants indefinitely.

This theory justifiably fills Breyer with righteous disgust.

Oddly, Alito then chose not to address whether this interpretation of the statute rendered it unconstitutional. Instead, he sent the case back down to the lower courts to re-examine the due process question. But in the process, the justice telegraphed where he stands on the issue by attempting to sabotage the plaintiffs on their way out the door. In the lower courts, this case proceeded as a class action, allowing the plaintiffs to fight for the rights of every other similarly situated immigrant. The government didn’t ask the Supreme Court to review whether it was proper for it to litigate the plaintiffs’ claims as a class. But Alito did it anyway, strongly suggesting that the lower court should dissolve the class and force every plaintiff to litigate his case by himself.

Alito’s antics infuriated Breyer, who dissented along with Justices Ruth Bader Ginsburg and Sonia Sotomayor. (Justice Elena Kagan recused, presumably because she worked on the case as solicitor general.) Using Zadvydas as a jumping-off point, he interpreted the statute to require a bail hearing for immigrants after six months’ confinement—provided they pose no risk of flight or danger to the community. “The Due Process Clause foresees eligibility for bail as part of ‘due process,’ ” Breyer explained. By its own terms, that clause applies to every “person” in the country. Thus, the Constitution only permits the government to detain these immigrants without bail if they are not considered “persons” within the United States.

That is essentially what the government argued, asserting that immigrants detained at the border have no rights. This theory justifiably fills Breyer with righteous disgust. “We cannot here engage in this legal fiction,” he wrote. “No one can claim, nor since the time of slavery has anyone to my knowledge successfully claimed, that persons held within the United States are totally without constitutional protection.” Breyer continued:

Whatever the fiction, would the Constitution leave the government free to starve, beat, or lash those held within our boundaries? If not, then, whatever the fiction, how can the Constitution authorize the government to imprison arbitrarily those who, whatever we might pretend, are in reality right here in the United States? The answer is that the Constitution does not authorize arbitrary detention. And the reason that is so is simple: Freedom from arbitrary detention is as ancient and important a right as any found within the Constitution’s boundaries.

Unfortunately, Breyer is not quite right that “no one” could claim, at least since “the time of slavery,” that noncitizens held in the U.S. “are totally without constitutional protection.” Just last October, Judge Karen L. Henderson of the U.S. Court of Appeals for the District of Columbia Circuit argued exactly that. In a stunning dissent, Henderson wrote that a pregnant, undocumented minor held in custody was “not entitled to the due process protections of the Fifth Amendment” because “[she] has never entered the United States as a matter of law … ” (The Due Process Clause protects women’s rights to abortion access.) In fact, the minor had entered the country and lived here for several months. But because she entered illegally, Henderson asserted that she had no constitutional rights. That’s precisely the “legal fiction” that Breyer rejected. It’s shockingly similar to the theory used to justify slavery and Dred Scott.

Do the Supreme Court’s conservatives agree with Henderson that undocumented immigrants detained in the U.S. have no constitutional protections? Breyer seems to fear that they do. In a striking peroration, Breyer reminded his colleagues that “at heart,” the issues before them “are simple”:

We need only recall the words of the Declaration of Independence, in particular its insistence that all men and women have “certain unalienable Rights,” and that among them is the right to “Liberty.” We need merely remember that the Constitution’s Due Process Clause protects each person’s liberty from arbitrary deprivation. And we need just keep in mind the fact that … liberty has included the right of a confined person to seek release on bail. It is neither technical nor unusually difficult to read the words of these statutes as consistent with this basic right.

We should all be concerned that Breyer found it necessary to explain these first principles to the court. So many rights flow from the Due Process Clause’s liberty component: not just the right to be free from arbitrary detention and degrading treatment, but also the right to bodily integrity and to equal dignity. Should the court rule that undocumented immigrants lack these basic liberties, what’s to stop the government from torturing them, executing them, or keeping them imprisoned forever?

If that sounds dramatic, consider Breyer’s somber warning about possible starvation, beatings, and lashings. The justice plainly recognizes that, with Jennings, the court may have already taken a step down this dark and dangerous path.