The two latest posts provide pretty good explanations of the argument. A more simplified way of thinking about it is that when you focus on one subset of discrimination ie race, class, sex, as the locus of oppression it ignores the role that the other avenues of discrimination play in overall subordination of certain people. For example, as the posters above me have indicated, saying that a black woman who is poor and also homosexual is oppressed due to her race is ignorant. All of these factors contribute to her subordination in society and when you say racism is the cause of this it masks other forms of discrimination and allows them to continue. ie if all racism were "abolished" would be on the same footing as a rich white heterosexual man. The answer is obviously no. An author named Crenshaw, I believe her first name is Rachel, writes some great articles about how all these forms of discrimination are mutually reinforcing and that it is impossible to overcome racism or sexism or classim without also addressing the others. This is a great argument Feminism, Racism, or Classism/Capitalism arguments because it short-circuits the solvency for their advantages while also allowing you to access a disad to their rhetoric or representation of the plan/alternative.
The alternative to these types of arguments is an analysis of the "intersections" of oppression and highlighting the dual nature of oppression. When I ran an argument like this, which was only once, my partner and I wore kilts and read cards about how men wearing kilts highlighted "crossing over" of oppression and showed that contemporary gender binaries are false. I know the Portage Northern/Central(not sure which one) guys a couple years back would debate in dresses. There are a lot of routes you can take but its a good argument that is straight forward and can give K teams some trouble.