Appeasement was based on several assumptions, some correct and some incorrect.

A European war would damage British interests, especially its ability to defend its empire. (largely correct) Britain had a variety of challenges before it including Indian nationalism and trade competition from the USA. (Correct) The Versailles settlement had broken down irretrievably. (largely correct) Britain could survive Germany becoming the dominant power in central Europe and could play Germany against the USSR. Hitler's aim was to over turn the Versailles settlement and this would be sufficient (wrong) It was easier to tie Hitler down with negotiations than to confront Germany militarily. (Wrong) It was sufficient for Britain to rearm defensively without planning on a major war

Clearly this was an appealing analysis for a generation of politicians who had seen the first world war. Many of them believed that blind adherence to alliances had caused the previous war and were determined to be more pragmatic. They were committed also generally anti communist and feared that Hitler would be replaced by a pro Soviet government if he fell.

There are some legitimate criticisms we can make even without hindsight. One is that Britain did not show a commitment to collective security and the League of Nations which would have made its policy more effective. Another is that the policy was fine for pre Nazi Germany but British diplomats and politicians were far too optimistic about Hitler especially by 1938.

Sources

Frank McDonagh, Neville Chamberlain and Appeasement (1998)

Keith Robbins, Appeasement (1997)

They were that confronting Hitler would lead to another war, which many Brits were afraid of after World War I. There is an argument that Neville Chamberlain deliberately appeased the Nazi's in order to give Great Britain more time to build up their forces for the inevitable war. Check out "Dirty Little Secrets of World War II"