Stupidity: Outside the bank, Mike and the first merc are having a shoot out across the parking lot. There is lots of room between them and around them. Yet a random construction worker, with a clear view of this shoot out happening, suddenly decides to take off running into the line of fire between the cops and the robbers and gets shot in the leg. Their was no reason for him to suddenly decide to run between them shooting at each other into the line of fire. (00:44:35)
Stupidity: During the gun battles with the "Tropic Thunder" actors, not one of the Flaming Dragon soldiers notice there is something strange about how the actors are firing their weapons (i.e, in the air, over the heads of the Flaming Dragons, etc.) or that there is no damage inflicted when the actors are shooting at or near objects in the area. Those two factors alone would tip off the Flaming Dragons that blanks were being used in the weapons of the actors.
Stupidity: In the Anubis universe, immediately around the time Lawless says, "Something's wrong," if you look closely, by Lawless, you see the two police officers behind Jet Li walk away to leave Lawless completely unprotected from behind. I understand it's a parallel universe, but that's some really bad police work to leave a prisoner wide open like they do.
Stupidity: Just after Joan finds Winslow after he kills a monster, they discover that it was actually a human geneticist, Dr John Carmack, that transformed into a monster, and they realise this by checking his name tag. Even if they didn't know the extent of what happened in the compound beforehand, the monster was still wearing human clothing and its body was still in the shape of a human body, so they should have, at least, realised that it was originally a human, even before looking at the name tag.
Stupidity: The mercs are said to drop in, in broad daylight. Approx four men are furthermore able to drop with plenty of ammo and at least one high calibre rifle, but they do not bring mines to secure roads nor drones to map the area.
Stupidity: During the final shootout in Saint's club, Lincoln (the long-haired hitman) sneaks up on the Punisher and fires at his chest with a shotgun at point-blank range, which does not harm the Punisher because of his body armor. Even though Lincoln could see that the Punisher was wearing body armor, he takes another point-blank shot at his chest to no effect when he had a clear head shot.
Stupidity: At the end of the movie during the shootout. Cops would not engage in automatic gun fire with dozens of civilians in direct cross fire. Why not get a chopper and chase them down a bit maybe in an open area with fewer civilians? Then maybe engage in gunfire.
Stupidity: After Roy escaped from the factory, he encountered a metal garage-door-type gate that was open at the bottom to the height of his knees. Trying to sneak away and in obvious pain from his injuries, it would have been quicker, quieter, and probably less painful if he crawled through the opening. Instead, Roy pulled downward on the chains, making a lot of noise, and it didn't even get the gate halfway up before he bent over to get out. The gate went up more after he stopped pulling on the chain. (01:15:29)
Stupidity: Becky possessed the mysterious key that the four neo-Nazi prison escapees were at the lake house to retrieve. Becky didn't know what the key was for, so did not have a vested interest in it. By first denying that she knew where the key was and later refusing to give it to Dominick, her father was killed. Had Becky simply handed over the key when Dominick asked for it, it is possible no-one would have been hurt/ killed. Becky keeping the key with no importance to her served to further the plot.
Stupidity: When they're tied up in the lab it's not that hard to escape. They have this loose straps with clips. (01:35:40)
Stupidity: During the battle on the harvester, Chani is firing an anti-aircraft projectile at a Sardaukar approaching her. Although the projectile is strong enough to destroy an ornithopter, instead of blasting the Sardaukar away, it pushes it into the air until it hits the harvester track. (00:36:39)
Stupidity: The Mentor told the Virtuoso that the murder of the CEO needed to look like an accident. It was acknowledged that 48 hours to plan the hit wasn't enough time, but it had to be done. The Virtuoso - supposedly an "expert" - decided to shoot the front tire while the CEO was driving past the building, making him "overcorrect" and thereby slam into the building. Even IF this would have killed the CEO, a BULLET HOLE to a front tire would not look like an accident. (00:09:22)
Stupidity: Early in the movie, AMMO and its crew show remarkable prudence in their approach to the drug deal, and a point is made about them following procedure, planning accurately using technology and trying to minimize collateral damage. The sting at the club goes against all of that. At the end of the day, it just consisted of getting close to the target and pulling guns on him in the middle of a crowd of civilians, the exits of the place (the front door even) completely unguarded.
Stupidity: Project Pegasus is a billion dollar structure with no security guards besides the couple dudes Fury shows the badge to at the entrance, no video surveillance, and once SHIELD arrives nobody has to even open a locked door anymore.
Suggested correction: First of all, Fury was allowed in as it's a government facility and he works for the government and as a SHIELD agent is allowed access. It's inside a mountain and they passed multiple security guards as they drove in, armed guards. Everything is thumb prints and cameras which was quite elaborate for that time. To say they lack in security is quite an understatement. SHIELD has quite some authority and can easily take control in the Pegasus project facility.
You are right about the main entrance being truly secure both for guards and strategic position. The problem is that they are free to just roam the facility for an hour, blast through doors, not a soul in sight, no evidence of camera monitoring the inside of the structure, and once the gag of the pad is finished, no door requires it. Actually, funnily enough you can see a guard of the place opening the elevator for Fury and the supervisor, as if the thumprint scan was needed to even get into the elevator itself, but Keller then just walks into the archive just fine (from a different door than the one Vers blasted). There are keypads to exit places (for instance the hangar, when the agents in pursuit break through the door you can see a keypad on the wall) but only when it's convenient (Vers and Fury walked through that same door with no problem, not to mention the fact that the whole stairs seem to have none, which is funny for a place that has keypads both sides of doors).
Stupidity: After Noah shoots the Humanity Bureau vehicle following them, they continue down the road and stop at an old abandoned building that still has some sort of running water in it. Lucas has to go to the bathroom so his mother just lets him wander off by himself to find a restroom. She doesn't go with him or make sure he's fine. And this is in an area where they know that most of the residents are hostile, and they are being chased by the Humanity Bureau. Noah even calls her out on the stupidity of her letting Lucas go by himself and she claims it's because he needed to do number 2 and that Lucas insisted and he's not a little kid any more... Which doesn't excuse the stupidity of the action of letting an 11 year old go by himself to find a bathroom in such a situation. And ultimately it does lead to him getting found by Agent Westinghouse. (01:08:30)