On Tuesday's The Five, a Fox news opinion chat show, in the wake of the Mall of America terrorist threat, Greg Gutfeld decried "gun-free zones" advancing the "more guns, less crime" argument that economist John Lott has more famously made.

Mr. Williams expressed incredulity. "I don't think that makes sense, that everybody in the mall has a gun. Let the police protect us."

Gutfeld laughed. There was banter. Some accusatory explanation. Oh, you lefties! But then Gutfeld regrouped.

"This is not an either/or - like everybody's armed [or] everybody's not. The concealed [carry] permit creates a level of uncertainty on the people that are choosing an attack."

There may be more than one reason why gun violence has plummeted over the past two decades. But one must be this: as Americans have accumulated more guns per capita than ever before, as more households possess guns than ever, the "celerity of punishment" (that old Benthamite term for swiftness of bad repercussions) has increased, nudging the marginally criminal to choose to commit fewer violent crimes.

Making society safer.

Since Williams seemed to have some difficulty with this, let's translate it for him: compare gun violence and peaceful gun ownership to viral infection and vaccination.