Steven Metz helpfully reminds  us that attacking Iran would be criminal and disastrous:
A pre-emptive U.S. military strike on Iran would ultimately be one of the worst strategic blunders in American history. That it is repeatedly considered by serious political leaders and security experts remains incomprehensible.
Attacking Iran would be wrong and horrible for all the reasons Metz gives, but what makes it unusually crazy is that the U.S. has no legitimate cause to go to war with Iran. Even if Iran were developing nuclear weapons, which it isn’t, that would not give the U.S. just cause to attack them. Iran’s conventional forces pose no real threat to the United States or our treaty allies, and there is no scenario in which the U.S. would need to “pre-empt” anything. An attack on Iran wouldn’t be “pre-emption” at all, since that would suggest that there is some imminent threat that needs to be eliminated. It would be a wholly unjustified war of aggression launched simply because our government can and decides that it wants to.
I submit that this is one reason why Iran hawks keep bringing up the possibility of an attack. It is an example of the kind of punitive military intervention that they think the U.S. can and should launch against “rogue” states to demonstrate that our government’s freedom of action isn’t limited by anything. Metz points out correctly that attacking Iran would violate the U.N. Charter and international law, but for the advocates of an attack the ability to violate international law with impunity is one of the things that appeals to them. It is not an accident that one of the most consistent and fanatical advocates for bombing Iran is John Bolton, whose seething contempt for international law and institutions is well-known. Advocates for attacking Iran (or any other country) don’t accept that U.S. power is limited, and they don’t want to accept any limits on U.S. action, either. If these people are still considered “serious” leaders and experts after all these years, that is a testament to how decades of ceaseless and illegal wars have horribly distorted our foreign policy debates.