racism and/as melancholia?

Cheng's explication of racism as “melancholia” challenged and confused me to great extent. The biggest trouble I am having is what exactly is is the object of melancholia. At one point, it seems like that racism is melancholia, or unproductive grieving over the “'loss' of the unassimilable racial other” (10). I interpreted this quote along the line of last week's readings: racial otherness as lack of normality or absence of property. This approach to define racism as Freudian melancholia further makes sense as the loss is proceeded and “digested by … American nationality” (10). But on the very next page, Cheng introduces another dimension of this melancholia. From this perspective, racism is a way to grieve on “... those moments when America is most shamefaced and traumatized by its betrayal of its own democratic ideology” (11). In this sense, racism as melancholia functions as tactic to minimize the cognitive dissonance between shameful past and the glorious ideal of the nation. What confuses me so much about the two dimensions of melancholia is that the latter – reflection and grief on the past – might serve as the remedy to stop the former form of melancholia. If we contemplate enough on the wrong and regretful deeds of our history and remind ourselves of the ideal, why we again repeat the same errors of the past and continue exclusion of “the others”? It would be really great if we could go over the basics of Cheng's argument on racism and melancholia and clarify the aforementioned confusions.