The original Ghostbusters script was written to be in the future. When it was first written, Ghostbusters were supposed to be like firefighters or police officers, a regular and everyday occurrence in society. However, once Bill Murray and the other stars read through the script, they figured it would work better if Ghostbusters were a unique group set in the current time period. You can say this worked out, as Ghostbusters is one of the best comedy movies of all time.