My takeaway from BNW was a warning against blindly embracing a society built only on good feelings and numbing anything that forces us to confront pain. The oppression was more or less a side effect of it.
Everyone in the upper classes were okay that lower classes were being oppressed because they all were just as happy thanks to Soma. The pain of the outsiders didn’t mean anything because they “chose” to live like that.
Genetic engineering was just a plot device to explain how the classes were chosen.