The movie does not go into classic black and white paint of character but rather shades of grey.
It portrays the good, bad and evil part in all of us. Parasite is within each one of us- some use it to get money while others extract services.
The poor family inspite of bad deceiving nature have goodness of thinking about others and supporting each others. While for surviving they even don't care about the lives of old couple in bunker.
The rich family despite being shown initially as caring, fire servents without explanation opportunity. The rich guy shows his evil part by caring about 'old raddish' smell more than lives of poor injured boy and girl.
The dream sequence in the end marks the beginning of new cycle of dreams and plans which never materialise according to poor Mr Kim.