Iran is nowhere the level of existential threat Germany was in 1938
What clearly is neither an existential threat to anyone, nor one within a country mile of that posed to Europe by Germany in World War II, is Iran today. Whatever their intentions, they haven't invaded a neighbor or annexed any territory. Their military ability (compared to Hitler's in 1938) is paltry. In 1938, Germany spent 12 times the amount that Iran does (in constant dollars) on its war machine, had probably the most sophisticated and efficient munitions factories in the world, and was inflamed with an ideology of regional conquest.
Iran neither has that ambition nor the ability to pursue regional conquest. Iran's current defense spending is about $15 billion a year. The United States' defense budget is $600 billion. (US and British defense spending were far behind Germany's in 1938.) Nazi Germany was allied with Italy and Japan, formidable military powers in their own right. Modern Iran has ... Syria and Hezbollah.
Other countries far outspend Iran on defense, including Saudi Arabia ($80 billion), the UK ($56 billion), France ($37 billion), and Germany ($42 billion) – all of whom would oppose a regional war of conquest by Iran.
The point should be made. People declaring a "Munich moment" typically consider all diplomacy and compromise as "appeasement." Either that, or they don't grasp the horrific consequences of World War II..
The frequent invocation of the 1938 Munich agreement between Hitler and Chamberlin in the debate over the nuclear deal with Iran not only is inappropriate because the threat from a nuclear Iran is nowhere near comparable to the threat from Nazi Germany, but also gets critical historical facts about the situation leading up to the Munich agreement wrong.