" Why would Iran want to do this?"
Not Iran as a country, Iran as the vehicle for Ahmadi-Nejad and his vision of being the representative of the 12th Imam on earth and becoming the "leader" of the Moslem world by wiping out Israel and thus meriting the position and admiration.
I don't sense that this guy is calling the shots. He's just a puppet for the uneducated and illiterate @sshole clerics over there.
That is probably the exact situation we face. He could care less about the Iranians, Syrians, Lebanese and Israelis. Even Saddam warned today that you cannot trust the Iranian leaders. Imagine that. A group of leaders that even Saddam thinks are untrustworthy.