Stupidity: Everyone laughs off any reference to the supernatural and the Ghostbusters being any more than hacks. However, they drilled a hole that unveiled a literal river of pink glowing goo that is even brought up at the trial; nobody investigates its origin or acknowledges the fact, which is exceedingly absurd since it involves heavy pollution of the underground system of a metropolis.
Stupidity: If the family is planning a big shopping trip, why would Clark still be in his morning clothes and busy putting presents in the attic as if he didn't know? And why wouldn't have anyone told him or reminded him before leaving the house? It just seems like a plot device using the foolishness of the characters to have him trapped in the attic.
Stupidity: The murder during the opening scene is ridiculous. Angela chases a screaming woman down an alleyway, in broad daylight, in front of crowds of witnesses, while driving a truck, runs her over, then throws her body in the back of the truck and then waits right next to the alley where she murdered the girl to be picked up by the van headed to the camp. At no point did any one of the numerous people on the street try to help the girl or even just investigate the alley to see if she was hurt (supposing it was an accident) or just call the police?