Sorry, maybe I'm being dense but--where? To me it looks like you take as given that racism necessitates social power and from that point argue for your thesis.

For example, this would be an argument: "Attitudes towards people of other races do not simply develop at an individual level, going no farther than personal interactions--from the beginning, race was used to justify institutional and societal oppression (slavery being the most notable example), not merely bigoted treatment of individuals. Racial bigotry expressed by individuals was just one manifestation of entire system of racism as a whole. Structural and cultural biases still exist, so we still need the historical name for racial bigotry backed by social power: racism."

That might or might not be a persuasive argument.

But you don't have anything like that that I can discern.