I’d argue that nobody acts with intelligence when first faced with a situation they’ve never prepared for, but usually by the end of the movie, at least one person learned enough to combat the disaster. It’s a steep learning curve when an alien psychopath is on the loose.
From what I recall of Alien, the stupid decisions made by the crew were understandable, considering how unprepared they were for that type of situation.
They bring back Kane after he’s been attacked by an alien breeder. Ripley didn’t want to let them aboard, citing quarantine protocol. Ash overrides her decision. The rest of the crew thinks he’s doing it out of mercy, but he had his own agenda.
When Ash tries to pull the creature off Kane’s face, it bleeds acid that eats through the floor and presents a hazard to the ship’s hull. That turned out to be a stupid decision, but they had no indication that kind of danger would result. They were trying to rescue their comrade.
They find the dead creature, and Kane appears to be OK. They had been contemplating putting him back in the freezer before he revived. They should have done so anyway, but they had been through a traumatic experience and wanted to get back to their regular lives. Besides, Ash, the secret robot, kept silent about Kane’s condition, because he had orders to bring alien lifeforms back and the crew was considered expendable.
A new creature tears out of Kane’s body and escapes. This blows their minds. They’re understandably shocked, and Ash prevents them from killing it. It gets away and they have no reason to think it would grow to such a massive size in such a short time. They learn of this new development when it kills Brett and hauls him away.
After heated discussion, the crew can only draw on their own experiences in controlling large wild animals. None of them have had training to do this. They don’t want to risk damaging the hull with projectile weapons. They’re showing caution. Their next best weapon is a flame thrower. They don’t realize the creature is more intelligent than a wild animal. How could they? It’s only a few hours old. There goes Dallas.
They discover the truth about Ash and how he’s been secretly aiding the alien. A fight ensues, they take out Ash after he taunts them. They realize they’ve been fucked from the word Go. They had been engaging in a lengthy boring mission and all the sudden their world has fallen apart and they decide they have to abandon ship. Was that stupid? They decided discretion is the better part of valor, and nothing they’ve done has been effective. Besides, they’re now down to three. Parker and Lambert are ambushed as they’re hurriedly loading supplies into the escape pod as Ripley prepares to launch. Were they stupid for hurrying? Parker wanted to incinerate the Alien, but Lambert was frozen in panic like a deer stuck in the headlights. He tried to save her but paid for it. Was he stupid for trying to rescue his friend? He had just lost his other crew members and couldn’t live with himself if he abandoned Lambert.
I’m not sure where their actions could be considered idiotic. Were the victims of Mt Vesuvius idiotic? The smartest thing for them was not to live there in the first place.