Screen Editor alex writes about how some kinds of disbelief are harder to suspend than others: 

Realism has a lot to answer for. For instance, the number of raised eyebrows I’ve received when recommending tv shows like Battlestar Galactica, Firefly, or Buffy the Vampire Slayer. Even when I talk about them in terms of artistic merit, interesting narrative structure and social relevance, more often than not I get a pause followed by “so it’s a show with alien robots/space cowboys/vampires?” Apparently some kinds of disbelief are harder to suspend than others.