I think this whole genre flirts with Capgras Syndrome, the basic identity perception malfunction behind concepts like changelings and many other "exact duplicates" or "tampering" scenarios which have malice as an optional component.

I think it is something that people are aware of, perhaps subconsciously, from cultural exposure. But, I also think many (most?) people have at least some personal experience of a similar sort. Not the full-blown delusional state, but an anxious moment of having feelings of recognition or safety turn inside-out as they realize things are not as they first appeared.