The following book was submitted by a site visitor and is a comprehensive and well thought refutation of the Christadelphian belief that references to Satan, the Devil and demons are simply personificiations of human nature and mental illness:
For the sake of comparison we include a link to a site which is a well compiled and comprehensive presentation of the Christadelphian position. This is the second version, updated February 2014:
My own thoughts are found in a section called Denial of the Supernatural and are brief. I believe the early Christians did believe in a spirit devil and spirit demons and it was not simply a belief in the personification of human nature. This is the simplest way to read the relevant passages. I would suggest the Christadelphian position is a rationalisation which has an appeal due to the worldview presented by modern science. The creative influence behind this interpretation owes its origins to a period called "The Age of Enlightenment". This is incidentally how it was seen by contemporary critics of John Thomas who often referred to his beliefs as "materialism".