NATO actually undermines the authority of the UN. The attack against the Libyan regime, as well as NATO’s participation in it, has drawn severe criticism, especially from Russia and China, who see the military campaign NATO and the UK, US and France undertook as overstepping the boundaries set by resolution 1973, against their explicit wishes. If NATO ever were to operate as the de facto military arm of the UN Security Council, then China and Russia would feel alienated from the UN Security Council, simply because they’re not (veto-wielding) members of NATO. [1]  [1] Rapoza, Russia and China Team Up Against NATO Libya Campaign, 2011