Stupidity: There is no way a fighter with a brain would risk serious injury to themselves before a fight by continually punching a frozen rack of meat in a freezer slaughterhouse. There is nothing to gain by doing this, and it would only result in both fists being broken.
Suggested correction: In fact, Sylvester Stallone permanently damaged his knuckles filming the two scenes. He obviously did not realise how dangerous punching a side of beef would be, and it isn't out of the question that the character Rocky Balboa wouldn't realise this either.
It shouldn't take a rocket scientist to know that if you punch or hit anything with a bare fist against anything solid, rock hard, you will damage yourself badly.
Absolutely, it shouldn't, but that is not what the "Stupidity" category is for. It is unintelligent for someone to do this, but that is not a movie mistake. Sylvester Stallone really did punch that beef and really did injure himself, so it is not something that is out of the question for a character in a movie to do.
No, but it is out of the question for a man with painfully damaged knuckles to go fifteen rounds with a world heavyweight champion boxer. In fact, Rocky would probably have failed the compulsory pre-fight physical and would have been ruled unfit to fight.
Where in the movie is Rocky experiencing "painfully damaged knuckles"? With your logic, the fight would have most likely been called long before the 15th round, due to the very unrealistic and improbable punishment the 2 boxers were inflicting on each other.
Stupidity: Why is it that runners wait until their 30th birthday to run, when they'll most likely get caught? It would make more sense if runners tried to escape to sanctuary weeks or months before their last day. This way, they could meticulously plan their escape without drawing attention to themselves.
Suggested correction: That wouldn't be particularly advantageous for runners. The computer system monitoring the city knows when someone is running regardless of their age and will dispatch the Sandmen to eliminate them. People who choose to run only do it as a last ditch effort, believing they will die on Carousel anyway so running is a risk some are willing to take. In the meantime it would be preferable to live out their guaranteed lifespan and enjoy the pleasures afforded to them by living within the city.
Stupidity: The babies could have simply been swapped at the start. There was no reason Father Spiletto needed to inform Robert Thorn of his son's death and then convince him to take a different child instead.
Suggested correction: Perhaps, but then again the Satanists were trying to cover all bases. If they simply swapped them, the parents may start questioning things when Damien grew up and they might have noticed that he didn't look or behave like either of them. For insurance they could have brought Robert Thorn into the plot (without his knowledge of the full story), so that if she asks any questions he could simply stick to the story, offering a cover to the Satanists. During the conversation, he mentioned that the baby dying would be devastating to his wife (which is why he agreed to the switch) so his intentions were pure, even though it ends badly and tragically for both him and his wife.