One of the hardest things to do in history is to read history in context, shutting out our foreknowledge of what is going to happen -- knowledge the players at the time did not have.
Apparently Neville Chamberlain is back in the public discourse, again raised from the dead as the boogeyman to scare us away from any insufficiently militaristic approach to international affairs.
There is no doubt that Neville Chamberlain sold out the Czechs at Munich, and the Munich agreement was shown to be a fraud on Hitler's part when he invaded the rest of Czechoslovakia just months later. In retrospect, we can weep at the lost opportunity as we now know, but no one knew then, that Hitler's generals planned a coup against him that was undermined by the Munich agreement.
But all that being said, let's not forget the historic context. World War I was a cataclysm for England and Europe. It was probably the worst thing to happen to Europe since the black death. And many learned folks at the time felt that this disaster had been avoidable (and many historians today might agree). They felt that there had been too much rush to war, and too little diplomacy. If someone like Britain had been more aggressive in dragging all the parties to the bargaining table in 1914, perhaps a European-wide war could have been avoided or at least contained to the Balkans.
There simply was no energy in 1938, no collective will to start another war. Even in France, which arguably had the most to lose from a reinvigorated Germany, the country simply could not face another war. As an illustration, one could argue that an even better and more logical time to "stop Hitler" occurred before Munich in March of 1936 when Hitler violated the Versailles Treaty and reoccupied the Rhineland with military forces. France had every right to oppose this occupation, and Hitler's generals said later that their forces were so puny at the time that the French could have stopped them with a brigade and sent them running back across the Rhine. And the French did nothing.
In addition, Britain and France had very little ability to do much about Hitler's ambitions in Eastern Europe anyway. How were they going to get troops to the Sudetenland? We saw later in Poland how little ability they had to do anything in Eastern Europe.
And finally, everyone was boxed in by having accepted Woodrow Wilson's formula of "self-determination of peoples." Building the entire post-war realignment on this shoddy building block is what really led to disaster. Emphasizing this essentially nationalist formulation as the fundamental moral principle of international relations -- rather than, say, the protection of individual rights of all peoples -- really empowered Hitler. In the Saarland, in the Rhineland, in Austria, and in the Sudetenland, it lent him the moral high ground. He was just fulfilling Wilson's formulation, wasn't he? These were all majority-German lands coming home to Germany.
Postscript: Years ago in my youth I used to excoriate FDR for caving into Stalin at Yalta, specifically in giving away most of Eastern Europe. I still wish he hadn't given his moral authority and approval to the move, but even if we stood on the table and screamed at Stalin in opposition, what were we going to do? Was there any appetite for extending the war? Zero. That is what folks who oppose the dropping of the atomic bombs on Japan get wrong in suggesting there were alternatives. All those alternatives involved a longer war and more American deaths which no one wanted.