For the most part, this is going to have to be written from Chamberlain's point of view at the Munich Conference. Much of the defense is going to have rest on the idea that history is only able to be understood at that particular moment. Political decisions are made at the time with only the information in front of the leaders at the time. They have to live with the consequences of their decisions and few paid a heavier price than Chamberlain.
One particular rationale for Chamberlain would be that the desire to avoid war is of specific importance. Chamberlain understood that emerging from the still very real shadows of World War I was reason enough to make enough bargains to avoid it again. Chamberlain cannot be fully faulted for wanting to avoid war, something that public opinion and worldwide isolation was still advocating. In this respect, if Chamberlain gets the blame, so does the majority of the populace who wanted nothing to do with war. Another reason for Chamberlain's optimism towards Munich was the belief with which he departed that diplomatic channels with Mussolini and Hitler would continue. His reasoning was that if these leaders were so bent on war, they would simply attack and would not return to the negotiating table. Chamberlain was too much of a gentleman to believe that Hitler was not. One cannot fully fault him for believing this and enabling his desire to avoid war as justifying his actions. Again, it was not as if Chamberlain was acting against the will of the British people who were excited at the prospect of "peace in our time."