The old saw about a liberal being someone who won't take his own side in a fight applies here. When the Bush administration presented evidence that the Iranians have provided material used to kill American troops in Iraq with roadside bombs, Democrats exploded in outrage -- at the Bush administration, for not being convincing enough, for having delayed the release of the intelligence, for being overly belligerent toward Iran, which just wants to talk to us.
To the contrary, Iran wants to destabilize Iraq so we will leave and Shia radicals will inherit the country. It wants to acquire a nuclear weapon to become the hegemonic power in the Middle East. And it wants to humiliate the United States and its allies at every opportunity. It can't merely be talked out of any of these goals. To the extent we try, we are ensuring the abject failure of diplomacy, which can succeed only after we demonstrate that we aren't to be trifled with.
The United Nations twice has passed resolutions sanctioning Iran for its illicit nuclear program. The first resolution banned nuclear-related exports to Iran but stopped short of banning travel by key officials. The second blocked Iranian arms exports and froze the assets of some officials and entities. Iran, understandably, is unbowed. After their initial hopeful suggestion that the hostage-taking was an honest mistake, the British got tougher. They banned their basically nonexistent bilateral business with Iran. In a few weeks, maybe the Brits will work themselves all the way up to strong-letter-to-follow.
At least that's what the Iranians expect. If we think the current course will ever fundamentally change Iranian behavior, the misunderstanding is all ours.