A wallet is reported 'stolen' in an office. Suddenly everyone is suspicious of each other. Every item formerly lost is now suspected to be stolen. You get your own wallet stolen. A month later when re-arranging your desk you find your wallet between the desk and the wall. You feel sheepish for your loud crowing about your wallet being stolen and how you too were a crime victim. You sheepishly keep quiet. Humans just act this way. The idea of what is 'a sane reasonable assumption' depends on a lot of things - information that one may or may not be processing in a completely rational manner.
From your response I can already feel what your response is going to be and I want to say I am not disagreeing with you I just think it's interesting how group think works - I myself am not immune.