It is true that Israel has a nuclear capability. That threat has at least kept Israel's enemies from launching large scale military assaults. It would not be rational to attempt to destroy Israel. If rationality always prevailed, there would be fewer wars.
Do you think a nation that paints the statement “Israel must be wiped out” on their missiles takes a rational view on Israel? Iran is also a direct sponsor of Hezbollah and Hamas.
"The range of our missiles covers all of Israel today. That means the fall of the Zionist regime, which will certainly come soon."
- General Mohammad Ali Jafari, November 2014