Commentary in Investor’s Business Daily nails the issue with an effective economy of words. From Tackling Tehran:

The U.N.’s toothless response to Iran’s defiance on nuclear weapons tells Iran it can do what it wants with no consequences. Once again, the U.S. is in the lonely position of telling a rogue state “no.”

The rest of the commentary is correct justification for that position, but the opening paragraph nails it without the need of further elaboration.