Zbigniew Brzezinski's op-ed on why we shouldn't start bombing Iran is truly excellent, but it's worth re-emphasizing the best reasons not to go to war; namely, that it wouldn't actually solve anything. At best, it would only set back Iran's nuclear program a few years and make the mullahs even more determined to acquire the bomb in order to deter the United States (at the moment, they seem to be divided on the subject; Supreme Leader Ali Khamenei has even issued a fatwa against actual nuclear weapons). It would also kill off the only long term hope of preventing a nuclear Iran, by making a real disarmament and non-proliferation agreement virtually impossible to put in place. And it would effectively prevent Iran from becoming a more liberal and democratic state anytime soon, which, as Shirin Ebadi pointed out, is the only other viable long-term "solution" here.
Plus bombing would kill lots of civilians, something that's worth repeating again and again. It would very likely escalate into a broader war. And all for something that's not even necessaryIran is almost certainly still years away from making a nuclear bomb, and even if it were to acquire one, there's little reason to think they'd try to destroy Israel or whatever else we think they'd do (as Matt Yglesias pointed out, when Iran had a chance to help Hamas out earlier this month, it responded with a token aid offering; oddly stingy for a regime supposedly hell-bent on wiping out Israel). We shouldn't be going to war with Iran ever. And for the time being, there's every reason to at least try and negotiate with Tehran.