From the post "The NRA, the Vatican, and the Arms Trade Treaty," by Paul Moses:

I'm not sure how I wound up on the list, but I received a robo-call from the National Rifle Association. An NRA executive urged that I oppose the Arms Trade Treaty the United Nations is working toward to regulate international trafficking in conventional arms.

I thank the NRA for focusing my attention on the issue. It seems to have passed me by that in 2006 the Bush administration made the United States the only dissenter in a 153-1 General Assembly vote to explore a treaty. The Obama administration reversed that position in 2009.

The NRA's phone call ended with a question that I was supposed to answer by pushing "1" or "2" on my phone: "Do you think it's OK for the UN to be on American soil attacking our gun rights?"

I didn't answer; the question is based on a false premise. The treaty would be aimed at setting standards for the poorly regulated market in importing and exporting conventional arms, not at weapons laws within any country. As a group of UN experts put it in a 2008 report: "Exclusively internal transfers or national ownership provisions, including national constitutional protections on private ownership within the State's territory, should not fall under an arms trade treaty."

From the standpoint of Catholic teaching, weapons control is a moral issue. That is how the Vatican framed it in a statement at a meeting on the arms treaty in New York in July:

  The Holy See recognizes the great importance of the current ATT
  process as it addresses in particular the grave human cost resulting
  from the illicit trade in arms. …