According to a theory of social psychology called the “weapons effect,” the mere sight of a gun inspires aggression. In 1967, the psychologists Leonard Berkowitz and Anthony LePage wrote, “In essence, the gun helps pull the trigger.” Their methodology had flaws, but later studies verified their premise. In one U.K. study, people were more inclined to assault a police officer who was visibly armed with a Taser. Brad Bushman, an Ohio State researcher who served on President Barack Obama’s committee on gun violence, told me, “We’ve found that it really doesn’t matter if a good guy or a bad guy is carrying the gun—it creates the bias to interpret things in a hostile way.” Citizens who openly carry firearms “think that they are making the situation safer, but they are making it much more dangerous.”