The non-producing couple were portrayed as being yuppies, which would be upper middle class. This is conveyed in how they dressed, their home, and how they spoke. It isn’t the wealthy elite, but the professional class below them. This contrasts with the poor group living in a trailer park during a time when trailer park trash was a common expression.

And I don’t think that “poor people shouldn’t procreate” was the message of the movie. However, the movie has a thesis from those first few minutes, intended or not, that making life safer and easier for everyone to predominantly lead to the dumb uncultured masses taking over well built systems until they degrade to the point where they don’t work any more.