James Joyner is against putting further sanctions on Iran. He argues that "sanctions make those enacting them feel like they're doing something but wind up hurting the very people we're ostensibly trying to help, the ordinary citizens suffering under repressive regimes." They are also hard to repeal:
As [Kenneth Katzman] explained in his talk, some sanctions fade easily. He gave the example of those that come with being listed as a state sponsor of terrorism by the State Department. The president can simply take a country off the list if its government changes. Otherwise, as was the case after Libya agreed to abandon its WMD pursuit, the president can order the removal pending a 45 day response period. Conversely, sanctions put on by the Congress or the United Nations can take years to untangle.