The Ghostbusters theme song might claim that they "ain't afraid of no ghost," but their clients sure are quaking in their boots. Our question is, "Why?" Besides the Gozer and its Terror Dogs, most of the ghosts are pretty harmless. More than anything they just seem to be nuisances that disrupt the order of things.
Oh, wait... that's it. Throughout, the movie shows us images of the supernatural world disrupting the world of the living.
In a whip-smart online article, "Overthinking Ghostbusters," Adam Bertocci points out how this motif of order vs. chaos pops up even in the very first scene.
Where do we start? A library, where every book is carefully alphabetized and cataloged, that is until the ghost of a disgruntled former librarian shows up. Books being reshuffled, ectoplasm dripping from the shelves, and cards of the card catalog erupting into a chaotic cloud—all these images come together to show the supernatural shaking up of the orderly world of the living.
These kinds of images keep popping up all through the movie. There's Slimer wolfing down gourmet food at a stuffy hotel, and the Ghostbuster's totally trashing the place to catch him. Then we've got the explosion that rips open the firehouse, a symbol of the order the Ghostbusters have tried to impose.
After this, things are so totally nuts, with ghouls crashing taxi cabs, monsters disrupting the subway, and police cars (symbols of order) being sucked into cracks in the Earth. Order has broken down and it's up to the GB's to restore balance.