Some reasons why it might be a good idea to destroy Iran's nuclear program:
1. Some states in the region mght shift their allegiances to Iran.
2. Iran’s regional rivals (Saudi-Arabia should be a given) will launch their own nuclear initiatives to counter an Iranian bomb sparking a nuclear arms race.
3. A nuclear-armed Iran would immediately limit US freedom of action in the Middle East.
4. To constrain its rivals, Iran could choose to transfer nuclear technology to its allies - other countries and terrorist groups alike.
5. Having the bomb would give Iran greater cover for conventional aggression and coercive diplomacy - battles between its terrorist proxies and Israel could escalate.
6. Iran and Israel lack nearly all the safeguards that helped the US and the Soviet Union avoid a nuclear exchange during the Cold War - secure second-strike capabilities, clear lines of communication, long flight times for ballistic missiles from one country to the other and experience managing nuclear arsenals.
7. Even if a nuclear-armed Iran would not intentionally launch a suicidal nuclear war the volatile nuclear balance between Iran and Israel could easily spiral out of control as a crisis unfolds, resulting in a nuclear exchange between the two countries that could draw in the US.
Then there is the question whether the US would need to contain Iran to keep the threat at bay. If so, the US would need to deploy naval and ground units and potentially nuclear weapons across the Middle East. Alongside those troops, the US would have to deploy significant intelligence assets to monitor any attempts by Iran to transfer its nuclear technology + devote a fortune to improve its allies’ capability to defend themselves.
The problem with this whole "let's bomb them to stop Iran from getting a nuclear weapon" thing is the simple fact that
Iran is not trying to get a nuclear weapon.
From Wikipedia:
http://en.wikipedia.org/wiki/Nuclear_program_of_Iran(emphasis mine)
What will lead to them wanting to develop a nuclear weapon is i
f we keep antagonizing them. If we stop antagonizing them, they have shown willingness to cooperate, especially now that Rouhani is President and Iran's economy is crippled by sanctions.
Now is the time to get things done via diplomacy rather than continue the warmongering that will only lead to a devastating conflict in the Middle East. We finally have the chance to end this, but for Israel's intransigence.
A simple strike on their nuclear reactors won't be like when Israel bombed Iraq's nuclear facilities back in the 1980s, where Iran will shrug it's shoulders and be like "okay, that's fine". Iran
will respond, whether it be sponsoring a wave of terrorism in Israel/Europe/the US, not helping us combat ISIS (who is an actual threat, BTW), or an outright conflict. Iran is a very powerful country in terms of military might, and any conflict will lead to the deaths of thousands of people, whether they be Iranian, Israeli, Europeans, or American; civilians or soldiers.
We are finally not at war in the Middle East for the first time since 2000, after $1.5 trillion spent on two wars, 6,500+ killed and 32,000+ wounded (the medical costs of which are enormous over the next few decades), and people already want another conflict to start over Israel's paranoia and Neocons' fetish for perpetual war?
We would have to invade, pacify, and rebuild Iran like we tried to do with Iraq and Afghanistan, and all it will do is inspire another wave of terrorism as "proof of our imperialist crusade against Islam" at a time when we can use our fight against ISIS to repair our relations with the Islamic world.
Life is not a Call of Duty game. Iran is a very powerful country, and starting a war with them is not going to be a low-intensity thing like Afghanistan or Iraq that will be a side story on the news. Additionally, we badly need Iran's help to fight ISIS right now.
Iran is not trying to get a nuclear weapon, unless we drive them to do so. I don't know why this is so hard for people to understand??