Back in 1967 the Doctor was tasked with identifying the Human Factor, which was to ultimately revealed as a plan to unveil the Dalek Factor (The Evil of the Daleks). But what is the Dalek Factor in reality? Fan wisdom states that the Daleks are the first of the Doctor's adversaries to warrant the "behind the sofa" moniker, but now a Cambridge academic has written a paper on what he believes really makes the Doctor's greatest enemy so frightening.
Doctor Robin Bunce has researched how the Daleks have been used over the years and the perceived effect on viewers, eventually arriving at the conclusion that our 'fear' of them is based upon how they challenge us on what it means to be human ourselves:
The reason the Daleks are evil is because we recognise that they were once better. They are the nightmare future we dread.
According to their back-story, once they were capable of genuine emotion and real moral good. Now they are sexless, heartless brains, shut up in machines incapable of intimacy, who have forgotten what it means to laugh and no longer think of themselves as individuals. We recognise the Daleks as evil because they have lost all that we hold most dear.