Over 20 years ago, I met Iranians for the first time at Brookhaven Nat'l Lab - women who were nuclear physicists involved with an experiment there. I had no idea that there was such a broad, technically educated middle class in Iran, despite the reign of the ayatollahs.
Two and a half years after the invasion of an essentially defenseless country, we still can't establish basic security, even around the "green" zone in Baghdad. If we invade Iran, all we'll do is strengthen the mullahs politically - and they won't particularly care if a million of their citizens die fighting the "western devils". Even the educated, moderate classes will look upon their soldiers as heroes in a holy and just cause.
Hagel may only be stating the obvious.
You're not going to get very far around here by being rational.
Invasion was never an option in Iran. That fact, alone, makes him an idiot.