From an Israeli perspective, however, the rhetoric Iran has directed aginst it leads them to think that Iran might not be deterrable, and that the Iranian leadership is so messianic that they might well use nuclear weapons against Iran even though it would ensure their own destruction as well. Here is an article from Jeffrey Goldberg outlining a number of cases when Iranian President Mahmoud Ahmadinejad has called for the destruction of Israel, likening it to a cancer that must be eradicated.
Furthermore, Ahmadinejad has called the Holocaust a lie, has hosted a conference where the truth of the Holocaust was debated, and suggested that the Holocaust was a fabrication designed by the victorius Western allies after World War II to embarrass the defeated Germany. Most recently, Iran's Supreme Leader Ayatollah Khameni stated that Israel was a "cancer" that would be cut off. Even the more moderate former President Hashemi Rafsanjani has called on Muslim states to use nuclear weapons against Israel, arguing that one nuclear bomb could destroy Israel while while the Muslim world would sustain "damages only."