I really wouldnt see it as such, maybe a mistake but not an epic screwup by a long shot. I think you may be looking at this through biased eyes, understandably, Winner.
Biased? Where? When?
If I wanted to be biased, I'd have started ranting about the French traitors who threw us to the wolves or something. I didn't. Sacrificing Czechoslovakia for nothing was obviously bad for everybody for the reasons I gave. It's a sort of tragic satisfaction to know that some light tanks the Germans have captured in 1939 in Czechoslovakia were then used during the campaigns in Poland and France.
You still neglect the fact that the British people would not support a war, and they could not prosecute a major European war without the support of the people.
The support was not much higher when the government declared war on Germany a year later, so I think this argument doesn't have much relevance to it.
We can speculate about the circumstances - let's say the British and French are more courageous - they say "no" to Hitler and instead make a deal with Czechoslovakia - the Czechs will give the Sudeten Germans a wide autonomy. Chamberlain isn't such an idiot as he was in OTL and he sells it as a great compromise.
Hitler is screwed - if he ignores the deal and invades Czechoslovakia anyway, there will be a formal declaration of war from France. This means that the USSR probably intervenes too (they had treaties with Czechoslovakia, but their help was tied to French intervention) and Britain will most likely follow suit. Alternatively, he backs off. Germany sufferes a diplomatic defeat, Hitler's position in Germany is slightly weakened and Germany doesn't get anything from Czechoslovakia. The West has more time to prepare, and so does Czechoslovakia and Poland. If the war erupts later, Germany will have much harder time winning it.
The British military was completely unprepared for war, especially the RAF. Sure Germany was weak at the time, but you can't assume your enemy is weak. And Britain alone has never been a military force on the continent without their ally, which was in even worse shape then them. Add to that the Commonwealth staying out of it and the British still had to worry about the Japanese and Italians taking advantage of the situation.
So? Germany was much weaker than it was in 1939, which means declaring a war against Czechoslovakia and the West would be something like a suicide.
As for the Western perspective: nobody had ever believed that Germany could defeat France in few weeks. They were not overestimating the Germans, they were UNDERestimating them, even after they saw what they did in Poland and Norway. They were not scared to death of German military might, they just didn't want to go to war because, well, war was unpopular at the time.
I am not saying the Western allies were ready to fight, no. I am saying that the balance of military strength in 1938 was much less favourable to the Germans, even if I discount Czechoslovakia, which would have been a tough nut to crack if it was allowed to fight.
The difference: France won the war. The point is that the British would have given the Sudetenland to a German state anyways, peacefully or after a war.
And you base this opinion on what, exactly? Which sources say so? (You don't have to give me links or names, I am not RedRalph. Just a general idea.) The so-called "Sudetenland" had never been a country, it had never been a part of Germany either. It was a part of Bohemia/Moravia. In 1918, there was no serious discussion about that (not even remotely as serious as the one about future Slovak borders). Bohemia and Moravia had clearly defined historical borders since the medieval times. Given the fact that the Germans in Czechoslovakia enjoyed more civic rights than the Germans in Germany itself, I don't really think that anybody could justify giving Sudetenland to Germany after a VICTORIOUS war against the German aggressor. That would be really absurd:
"We defeated you, but we will give your everything you want, here..."
And still Hitler's aggressive expansionism only became really apparent to the people after the invasion of Czechoslovakia proper, everything else was in protecting German people, which was viewed as acceptable. While yes, the government could and did see that Germany was going towards war (Chamberlain did), even with appeasement, but they bought time for the British military that had a lot more to worry about than just Germany, and France was vastly improved in the intervening year. Unfortunately Hitler did better.
For the third time: incompetence or stupidity doesn't justify anything. Anybody with a brain could see where it was heading - Churchill did as well as many other people. After the Anchluss, it was obvious that Germany wanted to expand.
Anyway, the fallacy of appeasment didn't die in 1939 either, it's been a part of British/French foreign policy ever since. Just look at what happened in Kosovo, Georgia, Israel etc.
Appeasement in any form is an Epic Screwup. Burke was right, when he said
"All that is necessary for the triumph of evil is that good men do nothing."
Yes they SHOULD have went to war then, or earlier, but it wasn't unreasonable to make that decision at the time.
Explain to me how going to war after annexation of the rest of Czechoslovakia would have been better. In 1938, Czechoslovakia had a relatively strong and determined military full of young men willing to fight the invaders. In 1939, Czechoslovakia's army was demoralized, the fortified border areas were now part of Germany and Slovakia's loyalty was seriously compromised.
It was totally unreasonable to sacrifice the only devout ally with a relatively modern and strong military that the Allies had in Central Europe. Again, anybody with some military insight could see that.
I am sure that for some spineless politicians in the West who only cared about the number of votes they'd get in the next elections, instead of long-term well-being of their countries, it seemed perfectly reasonable to ignore common sense and sacrifice some "far away country" they knew "nothing about". But then again, incompetence is no justification.