Stupidity: So if Harley Quinn drove the truck to blow up the plant, wouldn't she have had to drive through all the cop cars at the bar murder scene? We know it was the same street because the cop gives the necklace to the detective. (00:10:58)
Stupidity: When Joaquin was running from Cornell, he turned into an alley between buildings. He was to the left (of the screen), which was unobstructed, but ran to the right, so he could jump over boxes. Cornell could have also stayed to the left, but ran far enough to the right where he could kick the boxes out of his way. Easily avoiding the boxes would have been faster. (00:11:37)
Stupidity: When the police turn up the first time the mother lies to them to get them to go away but the burglars can't hear the conversation. She could have told them exactly what was happening and that she had to make it look like she'd got rid of them. She could have then smashed all the cameras and just let them in.
Suggested correction: This was a character decision, and a completely understandable one. Her daughter was being held hostage in the panic room. She decided to cooperate with their demands for the safety of her daughter. Your idea is a solid one, but she simply did not think of it in her state of mind. She opted to get rid of the police, and her decision is not a movie mistake.
Stupidity: Catherine, wearing a dress and coat, was outside in the snow chopping firewood while her teenaged son sat nearby playing video games on his tablet. This could also fall under "plot hole" because having the son close by made him available to try to help his mom when Pryce attacked her (with the intent to rape). (00:36:40 - 00:37:15)
Stupidity: The ending has a bit of a twist; apparently, octogenarian college professor Morgan Freeman somehow chased down and murdered offscreen 6'3" professional assassin Vernon Davis. That's not the toughest part to swallow, though; he also sent the two detectives (one of whom he is not even supposed to know of) via UPS 2-day delivery mail some body parts of his victim. We don't know which part Lavazzi gets (genitalia were mentioned earlier), but Boyd gets the eyes and decides to eat them. For starters, unrefrigerated 2-3 day old eyes would never look as pristine as the ones Boyd gets. Also, Morgan Freeman mentioned earlier in the movie that for the power of Muti to be effective, the body parts need to be taken from a victim that is alive, screaming, and eaten only mixed with herbs and other catalysts. So what the detective does doesn't make sense even in the movie lore.
Stupidity: Harrigan leaves his partner's badge on his grave where anyone could take it and use it to impersonate a cop or abuse it in other ways. (00:50:15)
Stupidity: There is a scene in which the phone rings back at the house and Andy goes to answer it. None of the henchman respond immediately, but instead WAIT for him to almost answer the phone before becoming making a move. You would think they would yell at him to not answer it or have one of them rush to guard the phone the moment it rings. Obviously the entire scene was done this way for the sole purpose of suspense.
Stupidity: The highly trained commandos who knew everything about the NSA base and penetrated it during a perfectly planned operation through weapons and devices that pierce steel like butter, decided to stand outside the barn (so they knew something valuable was there) and its wooden door. It even has a direct line to the command center.
Stupidity: Rick tries to kill Frank at his boathouse by dumping gasoline all over the place and using Ray Coleman's lighter that Frank had. At this point, Rick has gasoline over his arm, but instead of properly cleaning it, he opens the lighter immediately and has his arm burned. Surely a criminal genius like Rick wouldn't have risked this as this is a loose end. Further mention goes to when he has the bathroom door open for no reason while medicating the burn mark, which enables his wife to see him and discover who he really is.
Stupidity: The end fell apart. It took convincing to get the police at the picnic area; however, while Jack was cracking up, they just left alone with his gun. After the stakeout was a bust, why didn't the police just question the girl: "Who told you to come here? Who was to meet you here?" Also, they police see a smashed black station-wagon. Was there no connection to the previous child's drawing?
Stupidity: Molly was being hunted and didn't know if she could trust Rayburn when he encountered her. Rayburn told Molly that he wanted to help, wouldn't hurt her, put a blanket around her, and even carried her in the woods for some distance. When he put her on the ground (along with his backpack and rifle) to go find the rope to open the pitfall doors and had his back turned, Molly got out from under the blanket and hid nearby. Rayburn quickly found Molly, and Molly made a lame attempt at attacking him with some kind of club. The next day when Rayburn and Molly were in Rayburn's house and her hunter showed up and attacked Rayburn, Molly grabbed Rayburn's rifle and fired several shots at the hunter. Molly obviously knew how to use a rifle, so it was asinine for her to have hidden from Rayburn the previously night without taking his rifle (or the blanket). (00:36:22)
