It is probably the case that Iran pursued a nuclear weapons program until 2003. But that program was secret and it’s pretty obvious that Iran did not anticipate getting caught. Tehran has _not_ demonstrated a willingness to pursue an overt nuclear weapons program.
This matters because it makes an Iranian breakout scenario pretty unlikely. Furthermore, the more likely it is that Iran will be caught developing a nuclear weapon (through measures such as IAEA safeguards, intelligence methods, additional monitoring methods, etc.), the less likely it is that Tehran will try.
Put another way, some in Iran probably want a nuclear weapon, or at least a weapons option, but there is scant evidence that they want one at all costs. Therefore, Iranian officials’ preferences for a nuclear weapon are not immutable. Capabilities influence intentions.
As an aside, a weapons option may be troubling, but the number of people you can kill with an option is zero.
*Update:* Thanks a lot to Steve Clemons for the “link.”:http://www.thewashingtonnote.com/archives/2009/01/ventilating_tho/