What are the impacts on Iranian behavior of Western pressure? No one knows. The answer is never certain because the same pressure tomorrow may have a different impact than it does today: context is constantly evolving. What we do know is that the impact of pressuring and threatening an antagonist is highly complex. It also seems pretty clear that its real complexity far exceeds the understanding of most decision-makers. If the above picture is worth 1000 words for you, then you can stop reading.
But just in case you think the picture requires explanation...
Start with the center left square: "anti-Iranian pressure, threats, insults." Arrows should be interpreted as indicating that X covaries with Y. Follow the black arrows, for the moment ignoring the others.
According to the picture, as pressure tactics intensify, two things happen (black arrows): 1) the domestic political power of the Iranian "neo-con" war generation led by Ahmadinejad increases because when a society is attacked from the outside, it comes together in self-defense, 2) Ahmadinejad's status as a global Muslim leader increases because almost no one else is speaking up for Palestine, thus leaving him without competition (i.e., he gets a free ride as a "defender of the faith" and "leader of Arab(!) nationalism" without being forced to back up his words.
Whatever expansionist, adventurist temptations may exist in the Iranian elite, these temptations are intensified by the rising domestic political unification behind their threatened but increasingly famous leader. "I might prefer lower gas prices and freedom to go out for a drink, but ya gotta admire the guy standing up to the whole Western world!"
That is the core story of the picture, but it is only the first stage. Automatically, without any further action by anyone, additional things (blue arrows) start happening. Will the rising power of the Iranian war generation persuade them to be magnanimous and promote domestic democracy? That is theoretically possible. It is also theoretically possible that it will so scare everyone else that someone will succeed in putting together a winning coalition to shove them out of power. But the argument made in the picture is that as the regime's power rises, so will its dictatorial tendencies. If you think some contradictory trend might simultaneously occur, then the picture needs to be modified. In any case, the argument in the picture is that dictatorial tendencies will rise and, being of course noticed in the West, will promote still further Western pressure.
In addition, Ahmadinejad's rising international status will intensify Iranian aggressiveness. Why? Politicians tend to become more aggressive as they gain power: few ever know when to stop. That in turn will further stimulate Western hostility. Why? People seldom recognize the degree to which they are the cause of the effects they deplore. It is highly unlikely that Westerners who are making careers out of sounding the alarm about a future Iranian threat will, as evidence that they are correct multiplies, stop and recognize, much less admit that the Iranian aggressiveness they see might have been provoked by their insults, threats, and efforts to marginalize and discriminate against Iran.
With the completion of the second stage in the process, we now have two unintended processes intensifying the initial Western pressure. Forget real data. Just make the simplifying assumption that every action by any actor has the value of "1." Even before Westerners choose to take any further action, the value of their hostility is already "3" (the original "1" plus "1" from the top blue feedback arrow and another "1" from the bottom blue feedback arrow. In other words, the impact is intensifying pretty fast.
But that is just the beginning. All actors in the system are linked. Israeli politicians are watching and reacting to the behavior of Iranian politicians. If all Israelis are highly educated observers (such as Ilan Pappe or Uri Avnery), then perhaps they will reason that they must try extra hard to calm the waters of international discord when Iranian dictatorial tendencies and international aggressiveness rise. However, if there happen to be any expansionist tendencies in the hearts and minds of any members of the Israeli elite, the view of an increasingly dictatorial and aggressive Iran will almost certainly whet their own appetite for militarism and aggression. Arguments to the contrary can be added to the picture and evidence to the contrary would be most welcome, but that at least is the argument the picture makes.
This brings us to the third stage (red arrows): as Israeli elite aggressiveness rises, their hostility toward Iran will also rise. Is this logical? Well, no; that you adopt an expansionist policy should be be connected to your feelings. A professional should maintain a solid firewall separating policy from feelings, otherwise hubris will result. But the picture is not presenting a story about logic; it is presenting a story about how politicians can be expected to act, regardless of their culture or nationality. For those who want to turn the above picture into a mathematical (system dynamics) model of the dynamics of threats against Iran, we now have a value of "4" on the original Western threat (after a single threatening act). That is, the impact of threats will rise four times (according to this simple picture) as fast as you would expect! For those who want to model this, the result will be highly nonlinear, showing an exponential rise in intensity.
In theory, the mirror image is also true. If threats are very dangerous, a consistently conciliatory policy would in theory undercut tensions equally fast. Unfortunately, there is a problem: people tend to remember threats a long time, and people learn distrust much faster than they learn trust.