I have been remiss in delaying my response to Gary Robinson's comment on Iran and Germany. Oh well, that's life on the Z-list.
Let me first correct a small omission in my earlier post. It is a common principle of ordinary moral reasoning to consider an attack against one to be an attack against all; this standard justifies the use of force to protect others from aggression. It's apparently not common enough, however, to justify my leaving it implied in my earlier post, therefore I'm making it explicit now.
Gary makes the case that my application of the "Czechoslovakia standard" is equivocal. I have to again draw to his attention my repeated disclaimers that I'm making a moral case as a philosopher and not a pragmatic case as a politician. There is no question that the invasion of Czechoslovakia unequivocally invokes the moral standard of (shared) self-defense; the only controversy after Germany's invasion was the pragmatic question of whether to invoke that moral standard and go to war. Indeed the West's inaction after Czechoslovakia makes a strong pragmatic case that we should consider any aggressive war to be an offense deserving of retaliation.
Gary proposes an alternative standard of "A high probability of a major catastrophe, if diplomatic action and the always-useless "sanctions" prove not to be enough."
This standard is flawed on three counts. First, it specifies that we should make our decision on the presumption that diplomatic action will fail. Second, it unjustifiably labels sanctions as always-useless.
More importantly, though, it asks us to make accurate judgments on probability. This standard is so useless that it can serve only as an ex post facto rationalization.
Our ordinary intuition about probability is so deeply flawed as to be completely useless, as the continuing economic success of casinos makes blatantly obvious. Even professional statisticians are prone to making intuitive mistakes about probability. Even when all the factors are known and one is careful to do the math correctly, our ability to make probabilistic judgments is very limited. We can, for instance, peer only a few days into the future with weather predictions. Those who wish to justify a war with Iran are asking us to peer years into the future regarding the behavior of human beings; any single individual, much less an entire nation, is least as complicated as the whole Earth's weather system.
I honestly don't know what sort of crystal ball folks like Gary Robinson and Infidel753 are peering into. I've worked with statistics and statisticians for years, I'm a very good poker player, and I have no clue whatsoever what the Iranians will probably do next week, much less years from now.
If my reluctance to murder thousands, perhaps tens or hundreds of thousands of Iranians on the basis of a hunch brands me as a "dangerous extremist", I'll wear that label proudly.
 What about the United States' aggressive war against Iraq? I stand by the standard; you do the math.
 update Sanctions and inspections were effective in persuading Iraq to destroy its chemical and biological weapons of mass destruction and dismantle its nuclear weapons research infrastructure. end update What was that you were saying about "always" in your comment, Gary?
 I'm using "reluctance" in the sense of "unspeakable moral horror".