Stupidity: The security system is able to automatically ascertain the malfunction to the exact valve, and the electrical problem, but the alarm is not triggered at that point, but only when the holding cells are already filled with water and Breslin is making his return. They are on a ship, the fact that it's taking on water feels like a pretty important issue to monitor.
Stupidity: Crystal knows she is being hunted and in a very dangerous life-threatening situation yet, after she kills "Ma and Pops" in their Main Street Market, she grabs only a few shotgun shells out of the open box instead of taking all of them or as many as she could find. Also, she walks some distance to the store but did not take anything to drink or eat. (00:27:00 - 00:27:55)
Stupidity: When Olivia said, "Momma. It's hot", she was wearing a long-sleeved shirt over her overalls and shirt. Her mom, wearing a sweater over a tunic top, replied, "I know, baby" and asked Steve to turn the A/C on in the RV, but the A/C didn't work. Instead of removing some layers, Steve opened some windows. Jay complained how hot it was, but he wore a hooded sleeveless sweatshirt over his T-shirt (and never took it off, even when outside in the desert). (00:09:31 - 00:46:00)
Stupidity: If Leo wants to kill his son's killer at any cost and no matter what happens, he should've gone directly to his House when the purge starts.
Suggested correction: He absolutely is headed there, but we see at least one incident where his path is blocked due to people out purging, and he needs to turn around. That detour caused him to go a different route, which led him to the mother and daughter. We even see him struggling with the decision on whether or not to help them. He decides to do so, and the rest of the movie unfolds as we see, but there is no mistake.
Stupidity: Like in a previous movie adaptation (and unlike the novel), Lombard finds out way ahead of time that only another 'Indian' is left besides him, and knows they have the gun, but he lead them to the last body turning their back and leaving the gun to them, against any logic and declared purpose. It makes even less sense in this version than in the 1945 version, given the outcome. In the novel, the gun is stolen from him.
Stupidity: After the Defranco "assassination" Rollie learns he is a target and survives two attempts on his life. But instead of leaving town or finding somewhere else to hide for the night, he spends the night in his own apartment (even though he was well aware the killers knew where he lived). As a result, his girlfriend is killed and he barely escapes alive.
Stupidity: For someone trained like "H", it was absurd that he would run down the center of the road toward masked gunmen and get shot multiple times. It was also ridiculous for him to have taken his son to a location that was potentially dangerous and put him in harm's way in the first place. (01:13:20)
Suggested correction: I'm not sure how much H was trained. If I recall correctly he's a skilled criminal, and all his "training" was faked so he could get the job with the company. Regardless... training or not, all that goes out the window when your child is being attacked. Paternal instinct took over and he was rushing in to protect his son. As for your 2nd point, it's made clear that his task was to simply stake out what was supposed to be a routine truck route. They had no idea the truck was going to be robbed.
Stupidity: All of Robbie's circuits have been burned out as a result of Morbius ordering him to kill the Id monster. The crew only has 24 hours to get the ship loaded and a safe distance away from Altair IV before it explodes. But one or more of the crew spends the little time they have fixing Robbie, a very sophisticated piece of technology, who is working the controls at the end of the movie.
Stupidity: Instead of breaking into Gordo's house, covering all the furniture in one room with sheets/thin blankets, and waiting for Gordo to return home in order to kill him via a "dramatic re-enactment" (in an adjacent room which was not shown to the audience), Bill could have taken Gordo anywhere to avoid getting caught or calling the police on himself. Had Bill taken Gordo to his already-"wrapped" motel room, he had enough injuries after the fight to claim self-defense against an intruder. (01:43:20)
Stupidity: After stealing the candy tin full of money, Joey gave it to Matt. Standing in front of the house, Matt opened the tin to see all the cash ($12,600). Joey asked him if anyone saw him, and Matt replied, "No. Let's go before they do." Instead of "hiding" the candy tin in his backpack, Matt carried the tin out in the open - and soon ran into a man wearing a security guard uniform.
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: When the Hilts discover they're 20' short of the trees, why wouldn't he "dirty up" his white/light tan pants so the tower lights wouldn't expose him so easily?
Suggested correction: Because he would look scruffy and dirty once he got out. He was the Cooler King and knew his way around after all.
I would suggest in the reality of the escape, light colored clothing would not have been worn so as to blend in to the night and the surrounding environment better. The light slacks were strictly for artistic reasons.
Stupidity: This highly trained squad of soldiers is sent into a known contaminated zone with all manner of chaos going on within in...and the second one of them sees a woman outside his APC he ignores a direct order and pops outside to see how she's doing.
Stupidity: Martino's plan involves walking across the desert for 200 miles, in a raincoat, dress shoes, and nothing to cover his head. That's just silly and probably needed no sabotage from the killer at all, but he realises his compass was broken and his canteen emptied when it's already too late to go back.That's no subtle sabotage, in particular the compass being shattered, glass included. He didn't even perform a rudimentary check on his survival kit. (00:50:00)
Stupidity: The building is supposed to be without power - at all since the generator has been destroyed - and life support machines are not powered up, but the 3D printers in every room are powered up - so that the good guy can squish the bad guy's head in it, and the elevators, so that the good guys can escape. What sort of hospital has its electric grid rigged in a way that the elevators keep working but critical surgical equipment goes dead the moment the power fails? (01:12:00)
Stupidity: When Will Smith and Gene Hackman are running through the railroad yard. Gene calls Will by his real name, "Will" and not by his character's name "Robert."
Suggested correction: You could be a little bit more specific, but I don't hear him say "Will" at any point during that run.