But what the gun lobby wants is more good guys -- normal average citizens like teachers and movie theater patrons -- to have more guns. That is why it has been fighting since the mid-1990s to block any science that might show the costs of lots of good guys having lots of guns might outweigh the benefits.

In 1996, some members of Congress tried to completely defund the CDC's National Center for Injury Prevention and Control, which was doing gun research, Live Science explains. Instead, lawmakers stripped $2.6 million from the CDC's budget -- the exact amount it had spent on gun injury research the year before. Congress forbade research that might "advocate or promote gun control." In 2003, Kansas Rep. Todd Tiahrt forbid the Bureau of Alcohol, Tobacco, Firearms and Explosives from giving researchers data about guns used in crime. Last year, the National Institutes of Health was blocked from funding gun research. The efforts have had impressive results. According to a letter to Biden signed by 100 researchers, the NIH has funded just three studies on gun injuries in the last 40 years. Hey, that's three whole studies, right? Hardly censorship! Well, the researchers point out that guns have injured 4 million people since 1973, while four infectious diseases have affected just 2,000 -- and the NIH has funded almost 500 studies on them. The letter protests that "legislative language has the effect of discouraging the funding of well-crafted scientific studies."

This was a direct result of National Rifle Association lobbying, NPR's Carrie Johnson explains. Former Emory University researcher Art Kellermann told NPR that while at Emory, he found that a gun kept at home was 43 times more likely to be used in the death of a member of the household than it was to be used to defend the household from a bad guy. The National Rifle Association pressured Emory to stop Kellermann's research, but it didn't. Kellermann told NPR, "[T]hey turned to a softer target, which was the [Centers for Disease Control and Prevention], the organization that was funding much of this work. And although gun injury prevention research was never more than a tiny percentage of the CDC's research budget, it was enough to bring them under the fire of the NRA."

So far, the gun lobby has been quite successful in selling this. For evidence, look at the advice Chicago Mayor Rahm Emanuel, Obama's former chief of staff and a veteran of the triangulating Clinton administration, gave Democrats during a panel at the Center for American Progress. "Focus the argument on the criminals' access [to guns] and you're going to get a bipartisan majority," Emanuel said, according to Roll Call. "It's not about 'gun control.' It's about 'criminal access to guns.' That changes the debate."

Gun control advocates want to change the debate in a different way. Existing laws wouldn't have stopped the Newtown shooting, because Adam Lanza's weapons were purchased legally by his mom. She was theoretically a good guy -- a regular, law-abiding citizen -- with a gun. According to several national polls, the shooting has increased the public's desire for gun control, including an assault weapon ban. But most people who are killed by guns aren't killed in a mass shooting or with a military-style rifle. The NRA has an incentive to limit how much the public knows about how guns affect average anonymous people. Science and knowledge can be very powerful. Just ask the tobacco companies.