The conventional wisdom in Washington is that tougher sanctions are necessary to prevent Iran from building the bomb. My view is the opposite. The imposition of punitive sanctions has failed to change Iranian policy in the past, and there is little prospect that more of the same will succeed now.
Don’t get me wrong. I agree with the aim of preventing Iran from developing nuclear weapons. A nuclear armed-Iran would be a grave security threat to the region and globally. A settlement of the nuclear standoff would be enormously beneficial to international security and to the cause of global disarmament.
Sanctions can help to achieve this result, but not if they are used solely for punishment. To be effective sanctions must be combined with incentives and security guarantees as part of a negotiated diplomatic agreement.
Read my recent analysis of Iran sanctions in Foreign Policy in Focus.
David Cortright 
The benefits of the sanctions are so enormous for Iran regeme that one wonders if the west is securetly working with Iran regeme to oppress Iranian people towards some unknown end and that is what a lot of people inside are thinking. Iran regeme could not careless what the west sanctions will be as long as they can mix the hardship of sanctions with whatever opperssion and lack of managment they impose on the people and blame it solely on the sanctions. There is no accounting for where the huge sums of money they receive from oil export is going and the chaos and black market created by santions is the best cover up for it. The tight information control of news and internet of course in the name of Islam is evidence of keeping the population as unaware as possible and give most the benefit of doubt .
I agree with those who say Iran regeme is buying time but the time is not for making the bomb but to get strong enough to overcome any uprising from within with as little as fuss as possible. There are many aspacts to the unique situation at this point in time which has to be thought of individually and as a whole.
Thank you for yr interest .
Good to remind us that sanctions do not come without costs, sometimes to innocent people who may suffer, but also in the backlash and rally ’round the flag effects that may benefit the regime being targeted. External pressures against Iran allow the ayatollahs to justify repression and blame their economic mismanagement on foreign governments. They generate patriotic support for the government. No wonder Shirin Ebadi and other Iranian human rights defenders oppose the sanctions.