When they find the single, they could simply just determine whether the single is from human for help or single from alien. One of the crew point out that they are only crew on a cargo ship. They are not professional persons who has sufficient knowledge to handle the situation if the single is from alien. They could simply report it is that they discovered an alien site so that personals who have sufficient knowledge can be sent to handle this situation. Well, they didn't. They send a team to investigate the alien site, and one of the team member Kane get infected by the parasite on his face. They have regulation which could isolate Kane to save the others. They missed this chance again. After they witnessed the corrosive blood penetrating layers of the decks, one of the crew member suggests they should freeze Kane with the parasite, so that they can bring him back to their base and deal with it. This is a good suggestion which can save entire crew, but they still somehow missed this chance. Later, Ash finds the alien is missing form Kane's face, they still decided to investigate the room to find the parasite with no protection for the biological and chemical hazards. They searched the room for the parasites with only a small touch. If I were one of them, I will turn all lights on. After they found the dead parasite, and Kane woke up, they didn't give Kane a medical examination. If they did that, the parasite baby will probably not able to rape Kane's chest when they having dinner together.
I can keep listing like this for a while, but I guess I have made my point clear. Lack of sufficient knowledge and common sense leads to the disaster. I mean even the cat can survive the alien attack, how could they fail? Does the cat really need their help to survive? Even Ash is literally using the crew to feed the alien, they should still be able to protect themselves and survive if they use their common sense to make their decisions. I mean they just let themselves get into the worst situation with horror elements such as blood, corrosive acid, face and chest raper, which seems horror to the audiences. The movie is a success if it is trying to present the helpless and hopeless situations when the ignorant facing unknown.