Dopplegangers
According to Holly Gibney's initial guesses, she thought that the killer in question may have been a doppleganger or "twin" of sorts to Terry Maitland. Which brings to mind a burning question I've always had of them. Why are they always usually & universally considered evil? Never understood it.
Yes there are people who believe as Holly observed that we each have a double, a twin of sorts in the universe, but again why are they almost always thought of as malevolent? Are we malevolent to them? Why are we the good ones & they the bad?