Scott Lemieux gets this mostly right:
It’s very simple. When it comes to Iran, “liberal hawks” need to either 1)explain in concrete terms what the threat to American interests is and — this is important! — what kind of military action can advance American interests and why, or 2)enjoy a delicious frosty mug of shut the fuck up. (And given their recent record of assessing American security interests and the efficacy of military force, perhaps some slinking away in shame would also be in order.)
Sorry, a threat to American interests, or anyone’s interests, is quite a stretch as a legitimate casus belli and reeks of pre-Iraq bushism.
If there is not a blatant act of violence or at least a force headed your way that is going to wreak destruction take option 2 above.