Amid heated debate, the Ebola virus came to the United States on Saturday, August 2, 2014, aboard a Gulfstream jet chartered by the Centers for Disease Control and Prevention. The virus was carried in the bloodstream of Doctor Kent Brantly, who travelled within an Aeromedical Biological Containment System—a hermetically sealed, transparent plastic tent that isolated the patient from the flight crew.

The Containment System is, at first glance, underwhelming; it looks like a transparent shower curtain that has been haphazardly tied onto a grid of PVC pipes, like an amateur greenhouse or a children’s fort. In fact, it houses an entirely self-contained artificial environment. After a patient’s stretcher is placed inside, the entry sleeve is typically clamped at two points, heat-sealed, and cut. Connected to a battery-powered high-efficiency particulate air (HEPA) exchange unit, the plastic walls encircle a negatively pressurized weather system, within which a patient can remain isolated for the duration of a flight. Gloved sleeves sewn into the plastic at strategic intervals allow medical personnel to treat the patient without breaking the bubble; a needleless intravenous system is used to minimize risk of puncture. Throughout a journey that took him nearly halfway around the world, Brantly inhabited his own private atmosphere.

Medical quarantine has its own architecture: levels of separation and isolation, nests inside of nests. The structure’s first level, according to Jonathan Richmond, a biosecurity consultant who spent thirty-five years at the C.D.C., consists of “not much of anything at all, except simple behavioral guidelines like, ‘Don’t stick things in your mouth.’ ” Biosafety levels three and four are typically reserved for airborne diseases. Ones that only spread through contact, like the Ebola virus, normally call for level-two containment. But because Ebola has no proven vaccine or cure, Brantly, who was transported to Emory Hospital in Atlanta, has been under level-four containment—a protocol that requires what Richmond calls “extraordinary engineering controls.”

In addition to the rigorous atmospheric isolation—in which a separate, filtered HVAC system maintains negative air pressure in the portable unit or hospital room, insuring that contaminated air cannot escape—level-four quarantine requires airtight seals around the doors, anti-microbial UV lights, and a chemical shower for decontamination purposes. To treat Brantly, the nursing staff, out of extreme caution, has also chosen to wear full-body Hazmat suits equipped with respirators.

Brantly’s isolation was voluntary and self-imposed, but the troubling ethical implications of involuntary quarantine were made explicit a few days after he left West Africa, when Liberia and Sierra Leone instituted military quarantines. Throughout the countries, troops have been stationed at the perimeter of affected villages to prevent people from entering or exiting. Freedom of movement has, in effect, been suspended—not just for those suspected of suffering from Ebola but also for anyone who may have been exposed.

The panic caused by the outbreak has led many Americans to wonder whether a regional quarantine might ever be imposed in the United States. In the past, the spectre of militarized quarantine detention camps has typically been the preserve of anti-government conspiracy theorists and Hollywood screenwriters. But in 2005, during the outbreak of H5N1 (bird flu), President George W. Bush seemed to consider the idea, describing the use of force to isolate regions of the country during a pandemic as one of “a whole range of options in the public-health toolbox for ways to achieve this goal of social distancing.” That same year, the C.D.C. proposed an update to federal quarantine powers, which would have required ships and airlines to submit passenger and crew lists to the agency upon request, and would have made due-process provisions for people subjected to involuntary quarantine. At the time, the agency stressed that any future quarantine within the United States would “almost always be voluntary, with incentives to cooperate.”

That claim was called into question just two years later, when Andrew Speaker, an Atlanta lawyer carrying a rare and potentially deadly strain of drug-resistant tuberculosis, became the first person to be placed under federal quarantine since 1963. The mandate sparked media furor, as the C.D.C. told Speaker that he was not allowed to return to the United States until a bio-safe aircraft could be chartered. It also highlighted the agency’s impotence, as Speaker promptly flew to Canada and drove unimpeded across the border into Champlain, New York. President Obama has since scrapped the C.D.C.’s 2005 proposal. If Ebola—or something even more contagious, such as pandemic flu—were to break out here, it is unclear whether mass quarantine would be enforceable under the United States’ current legal framework.

The larger and even more troubling question is whether involuntary detention for quarantine purposes should be enforceable at all. The legal theorist Jennifer Elsea has drawn parallels between the rights of the quarantined and those of American citizens who have been deemed “enemy combatants.” Both medically quarantined subjects and detained terrorist suspects are examples, Elsea’s work suggests, of how the rights of citizens can be put on hold for indefinite periods of time. If being held in a state of quarantine is legally comparable to being held as a prisoner at Guantánamo Bay, is quarantine something we should trust to protect us, or is it something we actually need protection from?

The A.C.L.U. has argued that trading liberty for security in the event of a pandemic is not only undesirable but also constitutionally dangerous and unnecessary. In 2008, the legal scholars George J. Annas, Wendy K. Mariner, and Wendy E. Parmet warned of “the false premise that public health is a law enforcement or national security problem that can be solved by limiting the rights and liberties of affected individuals.” In 2007, Barry Steinhardt , an A.C.L.U. spokesman, emphasized that, “in the vast majority of cases, sick individuals are the first to want proper medical attention and need no encouragement or state coercion to voluntarily isolate themselves.” As we have seen in the cases of Andrew Speaker and the West African victims of Ebola, however, such rational and altruistic responses to involuntary quarantine are by no means universal. Active resistance does occur, and when it does it poses extraordinary problems of control.

During the current outbreak, for example, a woman infected with Ebola was “rescued” from a hospital in Freetown, Sierra Leone, by panicked relatives convinced that she was being held for nefarious purposes. The relatives rushed the woman’s hospital room and removed her from the building by force, thus breaking whatever rudimentary quarantine might have existed between her and the rest of Freetown, a densely populated city at the nexus of several international air routes.

It might be easy to dismiss this as an incident fueled by ignorance or poor communication between authorities and citizens. But quarantine does ask individuals to pay a heavy price for the greater good—in some cases actually increasing their own risk of disease by not fleeing. The physical isolation of patients like Brantly is straightforward enough. But at the legal, political, and geopolitical levels quarantine becomes a much more nuanced challenge, one that embodies class and racial biases, ideas of purity and pollution, national identity, and the fine balance in civil society between “freedom from” and “freedom to.”