The real 'danger' of Iranian nukes is that they would remove for ever any possibility that the US or Israel (or anyone else) would attack Iran. Thus by their deterrent effect they would greatly restrict the military options of all Iran's enemies. The other side of the equation is that they would be very costly to build, maintain and secure. They also would limit the actions Iran could take because having nukes means you don't dare meddle too much with someone else who has them. Iran will no longer be able to risk any aggression short of nukes against the US and Israel, for example, as the fact that Iran possesses nukes would make a 'first strike' against Iran a plausible response to conventional aggression.
from the article: An alibi for the Arrow