An Iran nuke is not just a threat to Israel. It is a threat to the rest of the world. Iran has publicly admitted its intentions to DESTROY ISRAEL. Israel has never done such a thing. And yes we have nukes...we have had them for years...so CLEARLY they are for defense seeing as we have never used them! I doubt Iran would be able to say the same.
U.S. to defend Syrian rebels with airpower, including from Assad (Reuters)
from the article: UN passes new nuclear sanctions resolution against Iran