They were grifters. I don't know how anyone could argue otherwise, except to troll. The worst thing the wealthy family did was to discuss, behind their backs, their "boiled dishrag" odor and associate the smell with "people who ride the subway".
I read that Bong Joon Ho had to justify to producers his calling the film "Parasite" (as it was considered an insult to the impoverished family) by saying that the wealthy family was also a parasite, helpless and needing assistance for everything--but that is the very nature of an employer/employee relationship, from the outset. Both parties agree to a mutually-beneficial exchange of services for money, which is not at all parasitic. They were not abusive employers.
More than simply creating a situation that was beneficial for themselves, the grifter family was shown to have ugly, selfish attitudes. In the scene where they are getting drunk when the family was away, they showed contempt for their employers, calling them stupid and reading from the daughter's diary as they ate the family's food and drank their liquor.
The film itself contrasts the grifter family's getting drunk and dirtying the house with the memories of the previous housekeeper, differently desperate, and her hidden husband, who would sometimes enjoy the family's absence by dancing in the sunshine in the beautiful living room.
The film also makes the family's selfishness evident before they even met the wealthy family when it shows their anger that they're being docked 10% of their pay when 25% of the pizza boxes they folded were done incorrectly.
Anyone who would argue that their poverty and desperation justified their forging documents, creating situations that would get trusted, well-performing employees fired, and celebrating the owners' absence by calling them stupid as they consumed their groceries and got drunk on their booze while making a mess is someone who is similarly victim-minded and without conscience.
The only act that indicated any conscience on the part of the con artist family was during the birthday party, when the con artist mother asked her daughter to take food down to the basement to "feed them first". The son also showed some level of compassion when he went to the basement and acted concerned about the well-being of the (deceased) former housekeeper.
The con artists never displayed enough soul for me to have sympathy for them and the wealthy family did not display enough soullessness for me to identify with the grifters' apparent contempt for them. Anyone posting on DL would be much more hateful than the wealthy family if they hired someone who smelled bad. The family never mentioned it to them directly or said, "please clean up, you smell funny." They only mentioned it in passing to one another.
It was a well-crafted film, but the filmmaker was not trying to teach us any lessons. There were good (though privileged and clueless) people and bad (selfish, clever con artists who happened to be poor) people and conflict between them. The only message I saw was that perfectly capable and intelligent people applied their abilities in selfish ways and that the father was likely the cause of this ugliness.
