What is the main theme of this movie?

Gattaca's society is rich with discrimination. In the world of Gattaca, individuals are discriminated against on the basis of their genetic code. While genetically engineered individuals form the society's elite, those born by natural means are treated as inferior, second-class citizens. For example, 'invalids' are restricted in their ability to choose their occupation, as all 'invalids', despite their academic abilities, are only allowed to perform menial tasks. This is emphasized in the ironic quote "the best test score wasn't going to matter unless I had the blood test to go with it." This illustrates that the society is not a meritocracy, as an individual's self worth is calculated purely by their genetic makeup.