Worlds Apart - S1-E2
Stupidity: The bad guy kills the deputy in the swamp, then later sees a little girl who witnesses the killing run away. He then searches the boat for a weapon and runs off after her after he finds a machete, without even considering the officer's gun still in its holster. Abby proceeds to make the exact same mistake later when she finds the dead officer (meaning there's danger nearby) and hears the girl screaming and runs in the direction of the screaming without taking the gun to protect herself.
Stupidity: After Bernie discovers a treatment for the infection, radiotherapy, everything goes back to normal. Except the contagion is airborne (which is why they were going to flush the entire ship's atmosphere), so they're just going to re-infect themselves in a few hours. And there's only one room on the ship that can be exposed to stellar radiation, so there's no way to clean the atmosphere either.
It's Only Rock and Roll - S3-E11
Stupidity: When the gangsters show up at the house Pam and Dak Hampton are hiding in, Pam is captured. Dak then attempts to flee by running out the front door. What a dumb move. No surprise that he got captured as well.
Stupidity: Nora's dad believes in heaven and doesn't want to upload himself, because he wants to be reunited with his wife. When visiting Lakeview, he tells Nathan that Nathan's soul went to "real heaven," so he's just talking to a simulation. Which means there's no reason he can't upload himself. His soul will go to real heaven like he wants to, and he can leave a simulation behind for his daughter to be with. Everyone would be happy, but nobody makes that argument.
The Perks of Not Being a Wallflower - S1-E3
Stupidity: Superman finally smashes the weirdly strong bad guy through a wall, then goes to Lois, says "he's gone", and whisks Sarah to hospital. But he has no idea if the bad guy is "gone" or not - they've just had an epic fight, he has some sort of super strength / resilience, and for all Superman knows he'll come around in 10 seconds and finish the job of murdering Lois.
Suggested correction: Superman knows the 'strong bad guy' is close to his own strength. After fighting him, he knows what effect the crash through the wall would have had on him, if he was knocked out, and how long he would be out for. So he knew there was little risk of the guy coming around in 10 seconds. Alternatively, he X-ray scanned the area and saw the guy was no longer there.
Stupidity: "Rei" comes into the circle, having been champing at the bit to "turn him into a smear on the floor." She's wielding a sword, Kovacs is unarmed, and she...slices him a bit, instead of a quick killing blow.
Through the Valley of Shadows - S2-E12
Stupidity: Burnham and Spock find one person alive from the otherwise-dead crew, miraculously. They know Control can infect humans, they know how advanced it is, the entire setup screams "trap", and yet they don't even question whether Gant even might be under Control's...well, control. A simple scan would have turned up anomalies and they could have avoided what followed.
Stupidity: Why did Nadira decide to rewire Circuit instead of simply destroying or dismantling him? If she decided to simply destroy him, then Ransik and his army would have been victorious against the Power Rangers.
The Passion of Conner - S1-E28
Stupidity: For some strange reason, Conner powered down from Triassic mode before battling Zeltrax.
Recognition - S1-E17
Stupidity: After fighting Wootox in Sky's body, why didn't Cruger contact the other Rangers and inform them about the body switch? This would have spared everyone a lot of trouble.
Stupidity: In the flashback, Emily's sister takes ill while playing her flute. In the next scene, the sister is sick in bed and Emily now has the morpher around her neck, but she is in the exact same outfit. If the sister was forced to pass the legacy on due to disease, it should have taken more than just a few minutes or even hours to learn that.
The Tale of the Dream Girl - S3-E10
Stupidity: A boy walking through the bowling alley stops and lets Johnny pass, even though Johnny is supposed to be a ghost no one can see.
Storm Before the Calm: Part II - S1-E38
Stupidity: Shane could have easily avoided the blast from Lothor by simply flying away to dodge it. Instead, he just hovers over him and allows his Battlizer to be destroyed.
Stupidity: Characters repeatedly make note of how hard to kill the Wraith are, but sometimes, especially in the final episode(s) of season 1, they go down easily in a few bullets each, and then don't even regenerate as the characters turn their attentions elsewhere.
Suggested correction: It's explained that Wraith are easier to kill the less they've fed recently, and that in later seasons, with more and more Wraith waking up, fewer and fewer are getting chances to feed before they fight the Atlantis Team.
The Robinsons Were Here - S1-E4
Stupidity: Satellite dish falls, trapping people inside, and they can't even figure out a basic thing like digging a hole to escape. (00:43:52)
Suggested correction: I didn't see anything they could use to dig their way out. Plus Don was on the other side, so they knew they could just wait.
Stupidity: The Tomorrow People tend to enjoy walking into and walking out of most scenes rather than teleporting. In particular, when fighting and needing to run away, they'll teleport to get a better fighting vantage instead of teleporting out of the situation.
Stupidity: During the scene at the restaurant, Rose pulls the fire alarm. Then she and the doctor run through the kitchen, past several chefs who just duck and crouch into corners. This would easily be one of the stupidest ideas ever. If there was a fire, they would evacuate out the back door instead of just sitting there waiting to be choked to death. And if they knew about Auton Mickey, running out the back door would also be a lot more logical than just crouching down and waiting to be battered to death.