Update: This post was originally written after nine were killed in a shooting in Oregon in October. It has been updated after Wednesday's California shooting.
As you've no doubt come to realize, perhaps at the dinner table or while talking politics at a bar, that debate can get heated — sometimes very heated. We thought we'd help make it more civil by grounding either side in some facts and well-reasoned arguments.
Whether you lean toward gun rights or gun restrictions, here's your guide to the debate, in five arguments. And just maybe, it'll help you understand where the other side is coming from.
Argument 1: Would more guns prevent gun deaths?
Pro gun control: The data would seem to suggest it would not. The United States already has the highest gun-ownership rate in the world — an average 88.8 guns owned per 100 people, according to a 2012 Guardian analysis of United Nations data and a 2007 Switzerland-based Small Arms Survey. (The No. 2 gun-owning-country is Yemen, at 54.8.)
We don't have the highest crime rate among developed nations, according to that 2012 U.N. survey, but we do have the highest firearm-homicide rate, according to a Council on Foreign Relations analysis of that study and the Small Arms Survey.
In other words: Lots of guns don't seem to have prevented us from becoming top in the world in gun deaths. So why do we believe more guns would change that?
Pro gun rights: It's difficult to measure with any specificity how many mass shootings have been or, more importantly, would have been deterred if we had more armed citizens and relaxed conceal-and-carry laws. (Take the Uber driver in Chicago earlier this year, who was licensed to conceal and carry and who shot a gunman who was firing on a crowd of people, for instance.)
But pro-gun-rights economist John Lott Jr. wrote in his 2003 book, "The Bias Against Guns," that states with conceal-and-carry laws did have lower firearm murder and injury rates. He's also argued that guns can be a powerful deterrent: A research paper of his cites a 1986 survey in which 56 percent of felons across 10 state prisons said they would not attack a potential victim known to be armed.
Argument 2: Do more gun laws prevent gun deaths?
Pro gun rights: The data on this is incomplete. National Journal published a chart in August proclaiming to show that states with stricter gun laws — Hawaii, Massachusetts, New York and New Jersey — had fewer gun death rates. But when the Washington Post's Fact Checker team removed suicides from those gun deaths (which accounted for more than 60 percent of gun-related deaths in 2013), the results changed, sometimes dramatically.
In this new calculation, half the top 10 states with the lowest gun-death rates (per 100,000 residents here) have less-restrictive gun laws.
Pro gun control: Just because the data is inconclusive doesn't mean we shouldn't implement common-sense reforms that most Americans — even law-abiding gun owners — agree on, like universal background checks.
And that Washington Post analysis you mentioned? It's notable that the states on the bottom (the ones with the most gun deaths per 100,000 residents) generally have among the least amount of gun laws (those highlighted in blue).
Argument 3: Should schools arm teachers and guards?
Pro gun control: The Oregon community college where nine recently died wasn't a gun-free zone. Umpqua Community College allowed anyone with a conceal-and-carry permit to bring their guns inside.
But for argument's sake, let's say teachers and other staff in America were all suddenly armed. Even the pro-gun-rights National Rifle Association-backed 2013 task force on this topic found that there is no national training program and very few local ones to adequately ensure these guns are used safely. Training everyone would be a huge and expensive undertaking, and even then there's no guarantee that guns wouldn't be fired accidentally or in a moment of passion. A 2000 review by the Harvard Injury Control Research Center, for instance, found that guns in the home are more often used to threaten people the gun owner knows rather than to thwart crime.
Pro gun rights: Just quote Ben Carson. The retired neurosurgeon and top-tier GOP presidential candidate said a few days after the Oregon shooting: "If the teacher was trained with a weapon, I'd be much more comfortable if they had one than if they didn't."
Backing up that assumption are surveys cited by the National Association of School Resource Officers, which advocates for and trains school officers. The group made the case that armed guards have helped decrease school violence, citing a 2009 study that found the presence of school officers, who are sometimes armed, was attributable to a nearly 73 percent decrease in arrests involving possession of a weapon on school property.
Argument 4: Is prohibiting gun ownership compatible with the 2nd Amendment?
Pro gun rights: The highest court in the land doesn't seem to think so. In 2008, the Supreme Court decided 5-4 that the 2nd Amendment's stated "right of the people to keep and bear Arms" means you can own a gun for self-defense, striking down Washington, D.C.'s 32-year ban on handguns in the city.
Arguing for the conservative Heritage Foundation, George Mason University law professor Nelson Lund wrote that the 2nd Amendment clearly "recognizes the inalienable natural right to self-defense. Lawmakers may outlaw certain types of weapons, but they may not disarm the citizenry."
Pro gun control: Yeah, but many other times this question has been brought up in a court of law, there's been a clear and consistent pattern, according to the nonpartisan, nonprofit National Constitution Center. And that is this: The four liberal justices in that 2008 case and the federal courts have nearly unanimously ruled the 2nd Amendment, which refers to "a well regulated Militia, being necessary to the security of a free State," only protects states's rights to maintain militias and not an individual's rights to own any gun he or she wants to.
Argument 5: Do Americans even want more gun control?
Pro gun rights: Not really. When Quinnipiac University asked Americans that question in September, more people said they oppose stricter gun laws than support them, including independents.
In fact, for the past decade, Americans have been shifting toward viewing guns as the answer to gun violence -- not the problem. After a 2014 Pew Research Center survey marked the first time in two decades that more Americans supported the concept of gun rights than gun control. An August Pew survey found public opinion narrowly split but much closer than it had been for decades.
Americans are also showing their support for keeping our gun laws the way they are at the voting booth. When a 2013 vote in the Senate to expand background checks failed, voters congratulated Republicans who opposed background checks by ushering in one of the party's largest congressional majorities since the Great Depression.
Pro gun control: Yeah, but when you break down specific gun-control policies, Americans are actually in favor of a few key ones -- sometimes with overwhelming majorities.
Even though it failed in the Senate, making everyone who buys a gun go through a background check has steadily been supported by 80 to 90 percent of Americans. It even gets high marks among members of the National Rifle Association.
Support for banning assault weapons and large-capacity ammunition magazines also polls well, regularly in the 60-to-70 percent range. With numbers like that, there's no reason we can't pass common-sense gun control reform that many Americans agree will make us all safer.