Stupidity: Marta is shown to barf whenever she lies, and Blanc knows this. He should've asked her who did it right away. The entire plot of this movie is rendered unnecessary.
Suggested correction: That would only work if Blanc knew that Marta had knowledge of who killed Harland and if he came to the conclusion that Harland actually killed himself. Blanc doesn't know that Harland killed himself to protect Marta until Marta confesses. Also, this wouldn't have solved the "who done it" anyway, since Marta had no idea that Ransom switched the vials.
Stupidity: When Roy finally gets to the Lima project in the shuttle but can't dock, he just lets it drift away - he could have at least tethered it to the station to use it for his return trip.
Suggested correction: There is no way to know the reason why he did this. It's plausible, or even likely, that the pod was out of fuel. Not only that, but it could not dock with Lima because it was damaged, so it's likely that the damage played into the decision as well.
Stupidity: Adam, Hannah, and Megan [sitting in SUV with flat tire] saw the Man flashing his headlights, getting out, kicking his own SUV and ranting while holding a machete. Instead of fleeing, they got out of their SUV and saw the Man was wearing a welder's mask. When they returned to their SUV, they didn't lock the doors. The Man ran over, pounded on the front passenger's window and then opened the door. He stabbed Adam 36? times while the two girls just sat there screaming and one said, "Please stop."
Stupidity: After one of the policemen decides to jump over the railing and right into the angry mob (!), Arthur just easily sneaks by ducking under it and takes a nice stroll that will lead him through an unlocked door. Nobody in the mob he is part of decides to do the same, and you can also see that one of the policemen is turned towards him, but does not even yell at him or move. And of course, with the theater packed with the Gotham elite basically under siege by a mob and guarded by the police, the door is unlocked and unchecked. Why not. (01:02:55)
Suggested correction: The point is they were all too distracted by the tussle to notice Arthur ducking behind the barrier. No cop sees him. The angry mob is controlled by the barrier and not all that large so they haven't taken extra precautions to keep the mob at bay, yet. The door Arthur gets in is probably a fire escape and can't be locked for safety reasons.
I think that with an angry mob worth putting barriers and a big police dispatch, they'd tend to lock the door that is like a 20 feet of walk in a straight line. I mean, they have barriers in front of the stairs, but at the base of the stairs there's an unguarded, unprotected, unlocked door. It's just funny. Not even something in the back or around the corner, no; literally one step to the right of the blockade.
Stupidity: Denny removed a tray of chicken/capons from the oven, set it on the counter, cut off a piece from one chicken and threw it to Enzo (who caught it in his mouth). If the meat had just been removed from the oven, it would have been too hot to give to a dog and Enzo could have burned his mouth/tongue. (00:51:25)
Stupidity: When Amy heard Luce coming toward the kitchen, she "hid" his school paper and bag of fireworks in a kitchen cupboard, apparently while knowing Luce would be doing the dishes (and putting them away in the cupboards). Amy and Peter were on the patio (with the door open) just outside the kitchen when Luce was doing the dishes yet Amy made no attempt to prevent Luce from finding his paper and bag of fireworks (which he did). (00:16:20 - 00:21:00)
Stupidity: Dirk squeezed a long stream of lighter fluid onto the pile of Mario's clothes, then saw a necklace, which he removed (and potentially got lighter fluid on his hand while doing so). Instead of tossing a match from a safe (r) distance, Dirk crouched next to the saturated clothes and held a match near the bottom of the pile, risking burning himself. (00:06:40 - 00:07:21)
Stupidity: Despite the fact that the villains know exactly where Brogan is for the better part of the movie thanks to a tracer, and that they display constantly that they are able and willing to hit with bold military operations even to the point of hitting an urban area overruling law enforcement (apparently Clay has authority to do that too), Brogan is able to get undisturbed back in the US through his friend's plane. Considering he was officially marked as a rogue agent and killed 8 DIA operatives, it's hard to see how Baron's plane could ever land on American soil after a long intercontinental flight.
Stupidity: The marble somehow got under Don's skin at the bottom of his leg and was moving up the length of his body. Instead of heading off the marble in order to intercept and stop it from continuing up his leg, Don got a knife/box cutter and jabbed it into his skin near the bottom of his leg and trailed the marble, causing a long gash that served no purpose (other than creating a lot of blood and making a gory scene). The marble eventually exited his body via his eye. (01:04:40)
Stupidity: Angela ran over to her neighbor Mr. Charlie when she heard him come home. Angela was complaining that his son and friends make too much noise, do whatever the want, are bringing property values down, act wild/crazy, draw attention to everybody, and she doesn't want the police coming. These may be legitimate complaints, but the way Angela expressed them would bring down property values! Not only was she yelling in the street, she used "m-f-ing" several times, as well as other select words. (00:02:35 - 00:03:07)