Asked if he can put a percentage on how much less harmful snus is than smoking, Dr. Fagerstrom said, "There has been many authorities, the Royal College of Physicians in U.K. for example, and they say it's somewhere between 99 to 90 percent less harmful than smoking. And I do agree with that. That's the ballpark."
Fagerstrom says snus is automatically less harmful because there's no smoke and no inhaling, the cause of most tobacco-related disease.
"Let's say I'm a smoker, and I quit, and I go to snus. What have I eliminated in terms of harm for myself?" Stahl asked.
"It doesn't have any impact on the respiratory airways. It may not cause any cancer at all except for a possibility that it might slightly increase the risk of pancreatic cancer, which is not a very common cancer," he replied.
"No, but it's a pretty deadly one," Stahl pointed out. "Does it create more pancreatic cancer than smoking?"
"No, smoking has a higher risk," Fagerstrom said. "Even on pancreatic cancer…it is a reduced risk."
He says snus - which has the same level of nicotine as cigarettes - may raise blood pressure, but doesn't cause heart disease.
What about mouth, the gums or oral cancer?
"The funny thing is that with the Swedish sort of snus, it hasn't been found in studies that it does cause oral cancer," Fagerstrom said.
Unlike American chewing tobacco that does cause cancer of the mouth, Swedish snus is regulated by the government as a food product, so the levels of toxins and carcinogens are kept to a bare minimum.
That's why doctors in Sweden recommend snus to people who simply can't stop smoking, even though it's clearly an addictive substance.
They're following a controversial medical practice called "harm reduction," and groups like the Royal College of Physicians are pushing it for smokers, saying that less hazardous products like snus "can save millions of lives."
"At this point in time, I cannot say these products are safer," Karla Sneegas said.
In the U.S., health officials like Sneegas don't like the idea of "harm reduction" - where you use another tobacco product to fight smoking. She runs the anti-tobacco program for the state of Indiana.
"I think that these products are going to end up leading to dual use of cigarettes and smokeless tobacco products and we have no idea whatsoever what is the outcome, what's the health impact of someone not quitting and using both products," she told Stahl.
"In other words, you're saying if they do that, it could end up being more harmful?" Stahl asked.
"It could end up being more harmful. We don't know," Sneegas replied.
She's also skeptical of "harm reduction" because tobacco company executives promote it, like Susan Ivey of R.J. Reynolds, the company that makes Camel snus.
"Because I don't believe that 45 million Americans will quit smoking immediately - that we should pursue a harm reduction strategy," Ivey argued.