Right, so it makes sense that the US would be worried... not why the UN should sanction them.
I'm referring to the inconsistency. The implication of what you are saying is: "The UN only intervenes when it suits the US". To me that makes me think LESS of the UN sanctions, not more.
Your comment conveys another implication that UN is supposed to be impartial to issues between member countries. That cannot explain veto power of five permanent members of UN security council, which no other country has.
On consistency: I don't think UN, as a group of nations with conflicting goals, tries to behave in a consistent way, although people are free to blame it for its inconsistency.
B.R. Myer's talk explains the motive behind NK's nuclear program pretty well.
http://www.booktv.org/Watch/11315/The+Cleanest+Race+How+Nort...