In recent decades, advocates of gun control have taken their cause to court, bringing lawsuits that charge the gun industry with negligence because of how it distributes firearms. Large-scale traffickers, these suits claim, purchase guns in big batches from corrupt or irresponsible dealers, especially those operating in states with weak gun control laws. These guns are then moved to places with stricter laws, where they are sold, supposedly at high markups, to criminal buyers.

Advocates...