Jay Gatsby is literally a self-made man who came from poor origins and became financially successful. However, Gatsby felt he had to change his persona (self-made) and resorted to bootlegging, gambling, and drug trafficking in order to reach this level of success. The implication is that someone like Gatsby is more likely to achieve the American Dream if he uses illegal or even unethical means to do so. This is more of a comment on social limitations than it is on Gatsby's well-intentioned but illegal practices.
InThe Great Gatsby, Fitzgerald presents a geographic description of the "Valley of Ashes" in Chapter 2 following the description of the green light on Daisy's dock in upscale East Egg at the end of Chapter 1. The green light and East Egg represent a holy grail and the landscape of the social elite respectively. The juxtaposition of this elite landscape with the waste land of the Valley of Ashes suggests that while the American Dream can be in sight (or in mind), there is a stark and rigid border between the waste land of the masses and the upscale world of the successful.
This is a valley of ashes--a fantastic farm where ashes grow like wheat into ridges and hills and grotesque gardens where ashes take the forms of houses and
chimneys and rising smoke and finally, with a transcendent effort, of men who move dimly and already crumbling through the powdery air.
Gatsby is a rags-to-riches story. For him, Daisy is the holy grail, the American Dream. Although he goes to illegal lengths to pursue her, his naive perseverance is admirable. However, his idealization of Daisy creates an expectation of which even she can not live up to. In the end, Gatsby does not "get" Daisy. His obsession with Daisy, his "ends justifies the means" philosophy leads him down a dark and illegal path which ultimately contributes to his failure. Not to mention, part of Gatsby's dream of Daisy is her social status and this is associated with money. The green light echoes ideas of life, vitality, and money.
Gatsby is partly to blame but he is also struggling against social forces which make it much easier for Daisy to marry Tom. One conclusion to all of this is that the American Dream remains elusive for people like Gatsby. Another conclusion is that the American Dream has been corrupted because it is reserved only for those born into money. In other words, if the American Dream can not be achieved by legitimate or even honorable means, it may not be worth striving for. Or, for the American Dream to live up to its idealizations, some social, economic, and cultural changes would have to take place so that a dreamer like Gatsby would have the same opportunities that a brute, racist like Tom would.