Risky Business: Why Attacking Iran Is a Bad Idea

Military Risks

Iran could attack U.S. naval forces and commercial oil tankers operating in the Persian Gulf, especially in the Strait of Hormuz.
Tehran could use mines, submarines, small surface vessels, and land-based anti-ship missiles in the narrow waterway of the Strait of Hormuz. Iran is also believed to possess roughly 100 HY-2/C-201 Silkworm or Seersucker missiles on 8-10 mobile launchers currently deployed near the Strait.

Iran could attack U.S. forces stationed in Iraq, Afghanistan, and elsewhere.
Tehran could launch Shahab-3 medium-range missiles, possibly armed with chemical, biological, or radiological warheads, against American forces stationed in the Middle East. Iran could also persuade radical Iraqi cleric Moqtada al-Sadr, a Shia who has pledged support to Tehran in the event of a U.S. attack, to have his Mahdi Army attack American soldiers in Iraq.

Iran could use its proxy forces such as Hezbollah to attack Israel, topple the fragile Lebanese government, or terrorize soft targets like embassies, commercial centers, or American citizens.
Iran could attack Israel directly using its Shahab-3 missiles or prod Hezbollah militants to launch short-range rockets from southern Lebanon. Other Iranian-influenced groups such as Palestine Islamic Jihad, the Hezbollah-financed al-Aqsa Brigades, or the Damascus-controlled Hamas militants could also attack Israel or destroy the nascent Palestinian national unity government.

A truly effective military strike would be a time-consuming and extensive operation, thus increasing the risk of retaliation against American forces.
The Iranians have fortified their nuclear facilities with blastproof doors, extensive divider walls, hardened ceilings, 20 cm-thick concrete walls, and double concrete ceilings with earth-fill between layers. While American GBU-28 "bunker-buster" conventional weapons might be able to destroy these hardened targets, the U.S. would need to hit them many times to ensure total destruction. Retired Air Force Colonel Sam Gardiner, an expert in strategic war gaming, estimated that there are at least 400 "aim points" in Iran, 75 of which would require penetrating weapons to destroy.
Any setback to the Iranian nuclear program would be only temporary.
Without a long-term diplomatic solution consistent with international nonproliferation standards, a military strike on Iran amounts to an open-ended military commitment. The Israeli attack against Iraq's Osirak nuclear reactor in 1981 did not end Saddam Hussein's WMD activity and an American attack against Iran would assuredly not end Mahmoud Ahmadinejad's nuclear aspirations.

Economic Risks
Oil prices would go sky high--experts predict over $200 per barrel and $5 per gallon.
According to a tally by Oil and Gas Journal, Iran has the second-highest supply of untapped oil reserves in the world, an estimated 125.8 billion barrels. With these vast petroleum resources and its concurrent ability to disrupt shipments in the Strait of Hormuz--through which 40 percent of the world's daily oil exports pass--Iran could severely destabilize global financial markets.

A global economic recession could be triggered if Moqtada al-Sadr got involved.
Moqtada al-Sadr, a staunch Iranian ally, controls Iraq's 140,000-member Facilities Protection Service responsible for guarding oil pipelines and refineries. He could easily cut the oil flow off from Iraq in response to an American military strike on Iran. The loss of exports from Iraq and Iran combined would cripple the global economy. This would not only harm the most industrialized countries but also hinder development efforts in critically impoverished areas of Africa, Asia, and Latin America.

Humanitarian Risks

Conventional attacks would kill thousands of Iranian civilians.
Tehran purposefully built its nuclear facilities near population centers to deter potential attackers. Any claim that an attack on Iran could be accomplished in one day or that it would be "limited" or "surgical" ignores the enormity of the operation. There is no such thing as a "clean" strike on Iranian facilities located so close to population centers.

Should the U.S. use nuclear "bunker busters," civilian casualties would be incalculable and international condemnation would be universal.
The Bush administration has contemplated using B61-11 nuclear "bunker busters" against Iranian underground facilities to ensure absolute target destruction. Using a nuclear bunker buster would create massive clouds of radioactive fallout that could spread far from the site of the attack. More than a hundred thousand civilian casualties could easily result, according to nuclear experts.

Political Risks

Global determination to build nuclear weapons would be reinforced, possibly leading to a renewed arms race.
The unmistakable message of a military strike would be that the U.S. is willing to attack countries that do not possess nuclear weapons. North Korea has clearly indicated that its revived plutonium reprocessing activity and its nuclear test are a reaction to the American invasion of Iraq and a strike against Iran would likely strengthen Pyongyang's resolve.

An attack on Iran would undoubtedly strengthen hard line extremists.
President Mahmoud Ahmadinejad would consolidate his power to the detriment of moderate reformers like former President Mohammad Khatami. Long sought-after opportunities to undermine the radical clerics and encourage Iranian democracy would be lost.
The attacks would unite the Iranian population against the U.S.
The Iranian population, which remains generally pro-American, would vehemently turn against the U.S. following a military strike. The U.S. would lose a priceless opportunity to nurture a friendly ally in a troubled region.

Unknown Variables

American intelligence about Iranian facilities is inconclusive.
The International Atomic Energy Agency (IAEA) has identified at least 18 Iranian nuclear facilities, but reliable sources suggest there may be more than 70. It is possible that Iran possesses buried nuclear facilities that have escaped detection by American intelligence. After all, the U.S. did not find out about North Korea's underground facilities until much later, and Iranian nuclear activity at Esfahan, Natanz, and Arak was a secret until dissidents revealed it in 2002.

American intelligence estimates that Iran is at least five to ten years away from building nuclear weapons.
Taking military action against Iran would be a repeat of the mistake the U.S. made in Iraq in response to misestimates of Saddam's WMD program.

Text taken from here.