It is Iran that has been threatening to wipe out Israel - not the other way around. It is Iran that has been attacking Israel through its terrorist proxies Hizbula and Hamas. All of this, despite the fact that they don't even share borders with Israel. In short, if they seek weapons is not for defense - they have been on the offense already.
Roadside bomb kills five border officers in western Iraq (AP)
from the article: Iran: World can't block our atomic program while Israel has nukes