After serving dozens of gremlins in the bar, Kate asks Billy what they are. He gives her this non-response:
BILLY: They're gremlins, Kate.
Wow. Thanks for nothing, Billy.
But gremlins, both the creatures and the movie, are hard to explain. On the surface, Gremlins is a Christmas movie. The opening shot shows Kingston Falls as a peaceful winter paradise ready for a white Christmas. But things go from 0 to OMG before you can say "don't feed them after midnight."
Gremlins is both a horror movie and a black comedy. Are we supposed to be scared of the Gremlins? Are we supposed to feel bad for the people they kill, or are we supposed to laugh at their ridiculous deaths? As the girl from the taco commercial says, "Why not both?"
Gremlins isn't Neapolitan ice cream, where you can easily separate its flavors. Gremlins is a well-blended cookies and cream. You can't separate the Oreo from the vanilla, nor would you want to. Both flavors, the comedy and the horror, are meant to be sampled together.
Director Joe Dante knows this, which is why he left in Kate's horrific Christmas speech, even though Spielberg thought it was too dark for the movie. Kate's speech illustrates that the perfect white-bread suburbia was imperfect even before the gremlins arrived.
People still had dark secrets that are so ridiculous they're almost funny. They just didn't talk about them. The gremlins bring it all out in the open. They don't reveal anything that wasn't already there.