The problem is, that the situation is far more complicated.
If there is no invasion against Iran - and after the desaster in iraq or Afghanistan I doubt that there will be an allied invasion against Iran - the only other military option would be air strikes.
And this would help the mullah regime, because then the iranians will support their government against the foreign attackers.
The same happened when the arabs under Saddam attacked Iran and started the 8year Iran-Iraq War. With this action the Khomeini-regime was stabilzed, because before the attack there were many iranian parties and groups fighting for power. But when foreigner like the arabs attacked Iran all iranian groups stopped the inner-political fighting and fought against the foreigners. The same will happen here.
Also there is the question, if all iranian installations could be destroyed.
What will happen in Iraq, where the Mullahs from Teheran have extreme influence on teh iraqui shi Žites.
Their political party - the shiŽite Alliance was the winner of the iraqi elections - despite of all attempts of the western nations to push their liberal candidate, Mr Allawi (who failed bitterly).
Actually the sunnite minority causes so much problems in Iraq.
What will happen if the religious leader of the iraqui shiŽites, Grandajatollah Sistani (by the way, he is an iranian and gets much support from Teheran), decides to help the shi Žites brothers and sisters in Iran.
This could result in a total nightmare.
So - its really not easy.
The only effective solution would be an invasion and installation of a pro-western puppet regime.
But it seems that after Iraq there are not so many people left who would support such a solution.
Military attacks will fail - also embargos from western nations.
An embargo from China and Russia would impress Iran - but how likely is such an embargo?
Or the USA could raise their support for the MEK-terrorists, who already are operating from theire bases in Iraq and perform bomb-attacks in Iran, killing civilians.
But an open war would only help the mullahs in Teheran.