One of the world's deadliest businesses - the $55 billion-per-year arms trade - prefers to operate in the shadows. Bananas, cold pills and truck tires come with more market rules and international norms. This shameful gap could be filled by a United Nations agreement nearing completion in New York. The Arms Trade Treaty would require signatory countries to abide by clear rules on the import, export and transfer of weapons, ranging from small arms to air-defense systems. The aim is to bring a lethal, back-alley game into the open and curb sales to brushfire wars and terrorist groups. Think of Syria, Sudan and Somalia as prime examples where outside guns, tanks or helicopters are killing thousands. Governments, militias and guerrilla movements with the cash can buy virtually anything through brokers with the right connections. The United States, as the top seller of arms, has a special duty to improve this patchwork system. The Obama administration has pushed for approval of the treaty, a healthy break from the Bush White House, which favored a country-by-country approach that achieved little. But don't think this treaty is a slam-dunk. Gun-rights groups such as the National Rifle Association bristle at any mention of weapons controls and see the treaty as a threat to domestic gun ownership. It's nothing of the sort, and State Department negotiators have made Second Amendment guarantees an absolute red line" in talks.