Dissolution of America, Morality, and Virtuous Ideals
It's important to note that the America that is idealized is one that was built on Protestant ideals, which placed genuine religiosity (juxtaposed with the privatization of contemporary religion) and personal merit in one's work as the highest goals in life. It combined both spiritual (religious) and material (consumerism) ideals to create what was once, arguably, the greatest nation to have existed.
The American Dream, in essence, is an extension of the Protestant maxim where success is, by and large, a function of one's efforts. It bore the Western internal locus of control, where an individual becomes the master of his destiny, devoid of external forces.
It wasn't until the post-war boom, where America realized its 'civilizational' peak, when the American Dream no longer became an abstract concept, but a tangible ideal that was available to those who adhered to the principles of hard work and diligence.
As capitalism flourished unabated, America began to see the decline in religiosity. Religion, which puts the soul at the forefront of life, eschews overindulgence in consumerism, as materialism facilitates hedonism, which in turn degrades the soul.
Capitalism, which promulgates consumerism, places material prosperity as the highest goal in life, at the expense of everything else. Religion, therefore, cannot have a symbiotic relationship with capitalism, because of their opposing beliefs (one towards the spiritual, one towards the material).
Today, capitalism is not only an economic and political system, but a replacement for religion; where before one would worship at the alter, today one flogs himself at the corporation, showing his virtue through working ~50+ hours a week.
Fight Club depicted the polar extreme of minimalism as an objection to the extremes of modern-day consumerism, showcasing the material aspect.
American Beauty, on the other hand, depicted the spiritual degradation caused by modern-day capitalism through sexual decadence, homosexuality, hedonism, disregard for family, etc.