Among the many arguments marshaled in opposition to U.S. intervention in Syria, a prominent one is that the chemical weapons taboo is not worth saving. Writing in Foreign Affairs last April, the political scientist John Mueller suggested that the world should “erase the red line,” since chemical weapons generally produce far fewer fatalities than conventional weapons. Echoing this reasoning, the Harvard scholar Stephen Walt asked in The New York Times last week, “Does it really matter whether Assad is killing his opponents using 500-pound bombs, mortar shells, cluster munitions, machine guns, icepicks or sarin gas? Dead is dead, no matter how it is done.” These arguments are troubling. Like the taboo against nuclear and biological weapons, the chemical weapons taboo is well worth protecting -- and inaction in Syria risks eroding it.

It is true that over the past century, conventional weapons have killed far more people than chemical weapons. But if we are keeping score, conventional weapons have also killed far more people than nuclear weapons. Nobody doubts that conventional weapons can and do kill in large numbers -- Hutu extremists in Rwanda demonstrated the lethality of even simple machetes and hoes. But nuclear, biological, and chemical weapons are labeled weapons of mass destruction because they have a higher potential to kill or wound very large numbers of people compared with other weapons. If used to full capacity and under the right environmental conditions, chemical weapons are more lethal than virtually all kinds of conventional weapons. In the August 21 attack near Damascus, sarin gas killed nearly 1,400 people in 90 minutes and injured countless others -- the single most devastating assault in the last two and a half years of war.

But the lethality of chemical weapons is not the main reason to distinguish them from conventional ones. They belong in the same category as biological and nuclear weapons because they are primarily weapons of indiscriminate destruction.

Protecting noncombatants from intentional harm is the basis for much of international humanitarian law and nearly all traditions of just war. And nuclear, biological, and chemical weapons make discrimination between civilians and fighters virtually impossible. This is especially true in modern warfare, which is rarely conducted on clearly defined battlefields.

Civilians are likely to be the main victims of chemical attacks. The reason is simple: Chemical weapons have limited military value. They did not determine the outcome of World War I, and they played an indecisive role in the Iran-Iraq War. Troops that are targeted by chemical warfare have the ability to adapt quickly and immunize themselves with protective gear. Syrian rebels have already been seen carrying gas masks. Civilians generally do not have such protection, and so the main reason a country would use chemical weapons is to terrorize civilian populations and thereby divert resources from an insurgency and sap the morale of opposition fighters.

Moreover, chemical weapons are most effective when used in cities, where buildings trap gases and prevent wind and rain from quickly dissipating the poisons. Chemical agents may be deployed through delivery systems that produce no high explosive impact. As a result, civilians may not immediately sense the danger of a chemical attack as they might in a conventional bombardment. Standard civil defense protocols for conventional bombardments encourage civilians to seek shelter in basements. This response is particularly devastating in a chemical attack because many agents are heavier than air. People rushing into basements for refuge would in fact be congregating in areas where the gases would do the greatest harm.

Many chemical weapons, like nuclear and biological weapons, are also weapons of prolonged destruction. They have the potential to kill and maim not only large numbers of their immediate victims but others removed by space and time from the initial attack. The persistency of weaponized chemical agents -- the length of time they remain effective after dissemination -- ranges from minutes to weeks. Sarin, the agent used in the most recent Syrian attack, stays lethal for 30 minutes to 24 hours depending on atmospheric conditions. Other chemicals, including VX, which is mainly weaponized as a liquid and evaporates slowly, can last up to a month.

The Geneva Conventions protect those who enter the battlefield to care for the wounded. Yet first responders to a chemical attack cannot always detect the presence of lethal toxins when they lack the proper equipment. Without protective suits, they may be exposed to deadly agents on the bodies and clothes of the immediate victims. Unless they follow protocols for the treatment of contaminated surfaces, the responders risk spreading the contamination to medical treatment areas well outside of the conflict zone. In the most recent attacks, the Center of Violations Documentation, a network of local Syrian groups that has reported on incidents of violence and protest since the early days of the uprising, found that a number of paramedics died or became ill as a result of exposure while they were giving aid to the wounded.

Furthermore, through environmental pollution and genetic mutations, chemical weapons inflict suffering and death for decades and across generations. The U.S. Department of Veterans Affairs recognizes that spina bifida, “a defect in the developing fetus that results in incomplete closing of the spine, is associated with veterans’ exposure to Agent Orange or other herbicides during qualifying service in Vietnam or Korea.” In Halabja, a Kurdish town subjected to an Iraqi chemical attack in 1988, some of the buildings and much of the land remain contaminated. Doctors have found that the chemical attacks contributed to higher rates of miscarriages, birth defects, cancer, and severe respiratory ailments.

Many skeptics of the chemical weapons taboo note that since not all chemical weapons are the same, international responses should be calibrated to the specific context in which they are used. It is true that there is significant variation in how chemical agents are disseminated, how they inflict harm, the speed with which they act, and the longevity of their effects. But the chemical weapons ban does not and should not distinguish between types of chemical agents for two reasons. First, a simple rule is always more enforceable and effective than a complicated and qualified one. Opening up the ban by trying to identify specific exceptions and qualifications runs the risk of dramatically weakening the global prohibition. And second, while some chemical agents do incapacitate rather than kill, historically these have not been the agents stockpiled by militaries for use in war. For insurgents and terrorists seeking to level the playing field with more powerful adversaries, the incentive is to acquire chemical agents of maximum lethality.

The international laws and norms that protect civilians from being targeted have contributed to an overall decline in the frequency and intensity of war over the past several decades. The international community should thus be trying to widen the circle of bans on types of weapons -- including the most pernicious conventional weapons -- not narrow it.

Those who oppose a U.S. strike against Syria should not conclude that the ban against chemical weapons is not worth enforcing. The conversation should begin from the assumption that it is a vital norm, and then move to a discussion of how best to uphold it. A strike is one option, but there are others, such as coordinating a global diplomatic effort through the United Nations Security Council to push Syria, as one of the few holdouts, to sign the Chemical Weapons Convention immediately. As a party to the CWC, Syria would have to agree to inspections and ultimately to the destruction of its stockpiles. To do nothing or dismiss the significance of the chemical attacks on August 21 would be the wrong move, weakening a taboo that has served the world well.