Soledad O'Brien could not disguise her incredulity on Monday when dealing with a guest's proposal that the best way to prevent school massacres like Friday's attack at Sandy Hook Elementary was to do away with gun regulation.

"How you can say that people should have fewer laws and not more? it boggles the mind, honestly," O'Brien told author John Lott. "If you were to come here and talk to the people in this town, they'd be stunned by you."

In his book More Guns, Less Crime, Lott, an economist by trade, proposes that one consequence of firearms regulations is to increase the likelihood of massacres like the one this past weekend at the Newtown, Connecticut, school. Authorties said the shooter blasted his way into the school before killing nearly 30 people, carrying, among other weaponry, a "Bushmaster" .223 rifle.

"We only have very tiny areas in the United States which are these completely gun-free zones, and yet time after time, that's the place these criminals go," Lott said.

One example, Lott said, was James Holmes, the man accused of killing 12 people and wounding 58 others at a movie theaters in Aurora, Colorado in July; of the seven theaters near his home, Lott said, he chose the one that banned weapons from the premises, a reasoning O'Brien rejected.

"Let me stop you there," she said, cutting in quickly. "Here, again, a case where someone had a semi-automatic rifle. How do you know that he chose that because they banned guns. Have you talked to him? I have not seen anywhere, in any transcript, of anything he has said that he picked it specifically for that. He has not spoken to the media. How do you know that? You don't know that."

Lott also alluded to two school shooting tragedies in Germany -- a 2009 attack on a secondary school in Winnenden where a gunman killed 15 people, and the 2002 killing of 16 students at a high school in Erfurt -- to bolster his point that keeping guns from schools invites violence.

When Lott tried to reiterate that strict gun laws make public places into "magnets" for mass attacks, O'Brien cut in again.

"A rational person could say, that having access to a high-powered semi-automatic rifle is inappropriate," she said. "There's no reason to go deer hunting with that. There's no reason to have access to that. And that is the connection -- that these killers have access to those weapons."

Lott responded by attempting to downplay the capabilities of the shooter's weapon.

"These guns are just like any hunting rifle," Lott said. "The Bushmaster gun there would be the equivalent of a rifle that would be used for hunting very small game, like squirrels. It looks different on the outside, because some people like to have guns that look like military weapons, but it's not. It's like any hunting rifle."

However, at least some online reviews of the Bushmaster point to rifles of its type being used to hunt much bigger animals, like coyotes or deer:

You can use a .223 Rem for deer as long as your shots are not in thick cover. My niece shot one head on at 150 yards with a 55g spire point. It flattened the deer, penetrating the neck/chest, breaking three vertebreas [sic] in the spine and exiting ahead of the hind quarter.

Even as Lott pointed to Germany as an example of gun laws going awry, supporters of regulation are saying Australia -- which has seen no mass shootings since the country banned semi-automatic weapons in 1996 -- provides a better example for re-configuring U.S. gun policy. The ban was inspired by the Port Arthur Massacre, in which a 28-year-old man killed 35 people with several semi-automatic rifles.

However, even his country's success in curbing gun violence, former Australian Deputy Prime Minister Tim Fischer told ABC News Austraila Monday, hasn't helped him sell that message to his American counterparts

"I am making very little progress," Fischer said. "They just could not get their mind around the simplicity of having a harmonized shooter's license scheme and weapon registration scheme."

Watch O'Brien's interview with Lott, posted on YouTube on Monday by Think Progress, below.