Stupidity: Dane is a brilliant man who has invested countless millions (hence his billion asking price) and much planning into the operation. Yet he only makes one copy of the disk? Suppose that disk had been lost or broken? His whole operation would have been a total waste.
Stupidity: The entire plot hinges on a military facility that knows it's housing what's essentially a sentient world-ending disease, and that has the foresight and resources to build a containment room with a cyanide failsafe, having nothing else to stop said virus from breaking out beside the glass her room is mostly composed of. Once she's out of that room, she just has to run through an unlocked, labeled exit door and hop a fence. Where are the emergency bulkheads? Where are the armed guards watching the hallways? Why isn't that fence electrified? Why isn't she wearing a metal shock-collar at all times? Even if that glass was bulletproof and/or they seriously underestimated her strength, they'd still have to open the door to her room at various times to give and take her food, books, laundry and waste.
Stupidity: When Angela goes back to her house and finds that it's being sold, why are the cops letting her busybody neighbor hang around, ask her questions, and give opinions about her answers? If this were to happen for real, I think they'd ask the neighbor if she could identify her and then send her home.
Stupidity: In the scene with the water-jug puzzle, both Zeus Carver and John McClane initially suspect that the small carrying case contains a bomb. McClane goes ahead and opens the case, which confirms that it is a bomb (the electronic readout in the case even says: "I AM A BOMB. YOU HAVE JUST ARMED ME"). If they suspected it was a bomb in the first place, why didn't Carver and McClane immediately try to warn the dozens of pedestrians all around them to evacuate the area before McClane opened it? That would be a seasoned police officer's first instinct. Instead, McClane and Carver banter and bicker and never attempt to warn the public, even as the timer is ticking down.
Suggested correction: This carries over from the very first time McClane and Zeus talk to Simon on the phone (the "As I was going to St. Ives" scene). Simon tells the two not to run and McClane assures him they won't but that there are at least 100 people on the street, to which Simon responds "That's the point." McClane takes this to mean he can't just warn everyone or Simon will set the bomb off. They open the case because they don't know that doing so will arm the bomb. They wanted to know if there was a riddle or more instructions. Having the bomb be armed by being opened, complete with the pithy text "you have just armed me" was just a way for Simon to torment McClane. The bantering and bickering is of course, still pretty stupid but is consistent with how the characters behave for the entire movie.
Still, McClane's whole motivation in this movie is to save innocent people from death, which goes above and beyond his motivation in the first movie (which was to save his wife). What is the whole point of disarming the briefcase-bomb in the park if not to save the public? As stated in the original post, no seasoned and dedicated officer of the law would proceed without warning the public.
Except he was told specifically earlier not to do that. If he warned people of the bomb, it was implied that Simon would remotely detonate it. It can't be "stupid" of McClane to not warn people if he thinks doing so will get them killed. I agree that it is a trite movie cliche that a cop doesn't act like a cop would in the real world, but in the context of this film McClane's actions are consistent with the instructions Simon gives him.
Stupidity: Why would 006 put Bond in a self destructing helicopter instead of just shooting him? Being Bond's old partner, he of all people should know how good of an escape artist Bond is.
Stupidity: In the opening robbery, killing the third guard made no sense. Even if they didn't kill anyone, they'd still already committed a serious crime, that would result in lengthy prison time if caught. It makes no sense that they have no problem leaving witnesses when they're guilty of armed robbery, but don't want to when they're guilty of murder. If they didn't kill the third guard, their chances of getting caught would've been the same as if they didn't kill anyone.
Suggested correction: Leaving an eyewitness for an armored car heist is certainly risky, but leaving an eyewitness for an execution style double homicide is totally different. California had the death penalty at the time this film was set.
Stupidity: When Dr. James Harvey dies, there should be a body left behind in the manhole. After Kat and Casper revive him in his ghost form in the Lazarus, he comes out with a body (and clothing). One can assume that there are now two bodies of him, one alive and one dead. That would make an interesting article in the newspapers of the next day.
Stupidity: The secret service officer near the elevator gets shot right in the middle of his head by the Penguin mascot, and she drags his dead body into the elevator. Suddenly he's able to moan and groan and she shoots him again. The guy was very shot in the head, as in graphically. How is he suddenly alive enough to moan?
Suggested correction: A bullet to the head is not guaranteed to kill someone. Movies and video games have taught us that being shot in the head is instant death, but that just isn't the case.
Pretty sure you wouldn't wake up in seconds after a bullet to the head.
Correct. You probably would just lay there stunned while moaning and groaning... exactly like the scene depicts.
He didn't "wake up", he moaned. Which is 100% possible and actually happens quite frequently.
Stupidity: All those people at the bus station yet no-one reports a blood trail from the phone to the bathroom? There's even blood in the sink.