The paranoid in the film represents the anti-communist paranoia, which reflects the tyranny of the post-war McCarthy era. People are afraid of those "pod people" at first and they try to do something to resist them, like asking the doctor for help or trying to find the manipulator behind, but gradually they accept the fact and when they become fake human beings themselves, they even begin to turn other normal people into “pod people.” This situation is a metaphor of the social phenomenon in McCarthy era when people made accusations of disloyalty, subversion, or treason without proper regard for evidence. I think the circumstance and ambience are similar to what happened in the Culture Revolution in 60s China. At that period, people are crazy at removing capitalism out of the country through violent class struggle.
At the end of the movie, Dr. Miles Bennell is regarded as a psychopath, but we as audiences all know he is not. Chinese always say “Standers-by see more than gamesters”. Suppose I were the person who had listened this story, maybe I would see the teller as a lunatic, too. Human beings tend to think they are the center of the world, they make standards and criteria for everything and thus are used to seeing things from their own perspective. If someone is different from them, they will naturally consider him as an outsider and the abnormal. That’s actually a represent of selfishness and ignorance of human being. Thanks for the accident at the end so that other people believe what Miles has told them. However, not every time there exists an lucky accident. So I think we should jump out of the circle where we are staying all the time and inspect what is happening around us. Stop requiring others to follow your step. Maybe something abhorrent will be normal after a second thought. Everything has its value in nature.