Philando Castile worked as the cafeteria supervisor at the school where one of our friends sends his kids. Phil, as he was known, was reportedly widely beloved. He is dead, the latest in a growing number of black men killed by the police during a routine traffic stop, this one reportedly over a broken taillight.

Much has already been said about the role of race in these shootings. As Minnesota Gov. Mark Dayton said plainly this week: “Would this have happened if those passengers or driver were white? I don’t think it would have.” Neither do we. As President Obama observed, echoing Justice Sonia Sotomayor’s powerful dissent in Utah v. Strieff, deaths like Phil’s are not isolated incidents. Rather, “they’re symptomatic of a broader set of racial disparities that exist in our criminal justice system.”

While there’s no denying that race played a critical role in Phil’s death, we think it’s also worth highlighting the way his case is different than many of the others: He had a gun. According to his girlfriend’s account, he voluntarily told the officer who stopped him that he had a gun, and she reportedly told the officer that he was licensed for concealed carry. (Civilians are encouraged to volunteer this information in any interaction with the police). But evidently that didn’t matter. As he reached for his wallet, the cop thought “gun,” and he started firing directly into the car. (It’s important to note that we still don’t have the officer’s account of what happened, and there is no video of what transpired before Phil Castile was shot.)

This happened just a day after police in Baton Rouge, Louisiana, killed another black man, 37-year-old Alton Sterling. Sterling also had a gun; he apparently purchased it almost immediately before the shooting in order to protect himself.

If there is a lesson to be learned from these two incidents, it’s that the proliferation of guns promises to make already racialized policing far more deadly. As guns multiply, both police officers and civilians are ever more inclined to assume that everyone is carrying, and that assumption doesn’t leave a lot of time for sober thought and clarifying discussion.

There are good reasons why some police organizations have expressed concerns about liberalizing gun laws. Police groups have long been aware that reforms like background checks make cops safer, and that castle and “stand your ground” laws can make their jobs more difficult.

As if we needed another sobering reminder, Thursday night’s attack on police officers in Dallas—five officers are dead and seven more were injured—showed that police have difficult, ever more dangerous jobs. They are frequently placed in situations in which their lives are at risk, and they are, as the Supreme Court put it in the 1989 case Graham v. Connor, “often forced to make split-second judgments—in circumstances that are tense, uncertain, and rapidly evolving—about the amount of force that is necessary in a particular situation.” That very uncertainty is why the legal standard for the use of force by a police officer doesn’t require them to be perfect. It permits them to use force, even deadly force, when they reasonably believe a suspect is a threat to them or to others.

There are a number of problems with the way this “reasonableness” standard has been applied to police officers, who are usually afforded enormous latitude by the courts. Clearly the proliferation of guns in our everyday lives only exacerbates the problem, just as it has in self-defense law more generally. In Texas, an open carry state, it’s exceedingly difficult for police to discern who does and doesn’t have the right to brandish a weapon, particularly in a volatile situation like the one we saw Thursday night. (That difficulty likely contributed to the Dallas Police Department identifying the wrong man as a suspect in the shooting.) Put most simply: In jurisdictions that make it ever easier for civilians to be armed, it becomes ever more reasonable for the police to suspect that anyone, and everyone, is armed. The unsurprising result? The reasonableness standard becomes a race to the bottom.

Even if particular officer-involved shootings (like the shooting of Phil Castile) might seem unreasonable in isolation, it’s going to be harder and harder to say that a police officer is acting unreasonably in assuming that the guy with the gun can kill him instantly. As professor Rachel Harmon at the University of Virginia law school points out in an email, police officers cannot know or care within a split second whether a gun in the hands of a suspect comes with a permit, or whether it’s illegal: “Police fear legally carried weapons as well as illegally carried ones. Since generous carry laws likely mean that police will encounter more armed individuals, even randomly, as in a traffic stop, it’s time to think a lot more about the role gun carry laws might play in police fear and police shootings.”

The continued proliferation of guns means that more civilian-police interactions in which guns are brandished will be resolved hastily and with deadly force. It also makes it ever more “reasonable” for police to assume guns are always present. It’s a vicious circle.

These two trends—the increasing access to lethal weapons and a declining standard for reasonable fear by police—are on an indisputable collision course. We will either have more guns and therefore more police shootings, or we will somehow have to train police officers to believe that it is objectively unreasonable to be afraid of being shot in the split second they have to contend with an armed stranger. The shootings in Dallas are more likely to tilt the standard in the opposite direction and make officers more likely to think the people they encounter are out to do them harm.

This would all be an intractable problem on its own, but it becomes even deadlier when we layer in the obvious problem of implicit and explicit racial bias. Assumptions about the threat posed by a civilian suspect—and particularly assumptions about whether that person has a gun—will always affect people of color disproportionately. White men open-carrying might be terrifying to some of us, but they won’t generate as many calls to the police as black men carrying guns. That racial disparity is also evident in statistics about police-involved shootings. A report from October 2014 by ProPublica showed that young black men are 21 times more likely to be shot by the police than young white men: “The 1,217 deadly police shootings from 2010 to 2012 captured in the federal data show that blacks, age 15 to 19, were killed at a rate of 31.17 per million, while just 1.47 per million white males in that age range died at the hands of police.” The disparity holds even for unarmed black men. A recent study found evidence of “a significant bias in the killing of unarmed black Americans relative to unarmed white Americans, in that the probability of being black, unarmed, and shot by police was about 3.49 times the probability of being white, unarmed, and shot by police on average.” So long as race correlates with poverty, and with living in high-crime neighborhoods, the vast disparity between lethal police shootings of black men and their white counterparts will persist.

The profoundly sad lesson of Louisiana and Minnesota is that it is now objectively reasonable for black civilians to be ever more afraid of routine traffic stops. The lesson of Dallas is that it is also objectively reasonable for cops to be ever more afraid of civilians with guns. So we have mistrust and fear and panic on both sides, both apparently reasonable. But what makes these encounters lethal—as opposed to merely ambiguous and fraught—is the guns. And what makes it “reasonable” to use force in response to the reasonable fear, is the lethality of guns. This ends only in more death on both sides, death all couched in legal standards of reasonableness. And that death will always be racially disproportionate.

This need not be a conversation about whether you “support” Black Lives Matter or whether you “support” law enforcement. Supporting both is the only rational answer, and reason suggests it’s the very prevalence and lethality of guns that will continue to define legal “reasonableness” down.

See more of Slate’s coverage of the Dallas shooting.