This “Bomb them back to the Stone Age” line is a hackneyed cliché.
We’re not going to destroy a nation of 95 million, many of whom have suffered grievously under the regime. Aside from which, the most massive bombing raids (short of nukes) have historically had inconclusive results.
Nuclear weapons dropped on Hiroshima and Nagasaki impelled the Japanese emperor and military high command to surrender. However, the United States is not the only country to possess these weapons, unlike in 1945. The Pakistanis, Indians, and Israelis have them, as do Russia and China. Taking out Tehran this way would cause Pakistan to strike back, maybe on Bahrain, maybe on Tel Aviv. The Israelis and the Indians would retaliate with nuclear weapons against the Pakistanis. Russia would use this action to take out Odessa and Kiev. Then Russia and China would threaten either to blackmail the United States and NATO to back away or threaten a worldwide nuclear holocaust.
American first use of nuclear weapons would open a can of worms that would result in a disaster unparalleled in recorded history.