The debate over President Trump’s travel ban and the debate over gun control look surprisingly similar – except for who’s on which side. In each case, supporters of the policy argue that it’s necessary in order to prevent incidents of lethal violence, while opponents argue, first, that the policy’s likely impact on such incidents is overstated, and second, that it’s unjust to restrict the freedom of a vast group, most members of which are peaceful and innocent, merely on the grounds that a small percentage of that group’s members might turn violent. When the vast group in question is Muslim...