Why do atheists have such cynical personalities?

Cynicism is justified if reality is against that sort of preposterous ideology. But you're looking for the term rational scepticism, which is determined by the degree of evidence that gives it persuasive evidence and scientific weight. The lack of evidence for an inside job entails that I am highly sceptical of any inside job. The overwhelming evidence for the moon landings confirm that any explanation otherwise is to be suspect of conspiracy and myth.