Here's one reason that might justify a background check. It's pretty disgusting that an al Quaida terrorist or the member of a Mexican drug cartel might come to the United States to buy guns. They're foreigners and therefore have no 2nd Amendment rights. Plus, many of them are in the country illegally. The 2nd Amendment affords citizens the right to bear arms, not foreigners who have invaded for nefarious purposes. So should we make sure to check for citizenship before allowing the sale of a gun? And include that check at gun shows?