Accepting any dogma without question causes one to lose individuality and the ability for critical thinking. Every time this happens, people become part of an unthinking mob looking for leadership. This theme could apply to any belief or political ideology to the extent that one or the other tends to dehumanize the individual.
In Invasion of the Body Snatchers, the pod people represent a society whose individuality has been stripped away. They are bred for conformity and conditioned not to think or to feel emotions. In this regard, the movie is less about the threat of communism and more about the threat that conformity rather than individualism poses. Throughout the movie, the audience is reminded that conformity results in complacency and eventually apathy.
In the movie pace spores are taking over the sleepy hamlet of Santa Mira, California. Only the hero can stop it. In the movie Alien, the bodies of the crew of the space tugboat Nostromo are being taken one by one by an alien that attacks them and converts them into incubation chambers for its young. As in Invasion of the Body Snatchers (Invasion), aliens are present in the form of pods. The pods are the first stage of the reproductive cycle, but a human host is required to complete the transformation process. In both movies, when the gestation period is over the original host body is destroyed.