I have a feeling that you are reasoning from the premise that every aspect of our behavior must be either adaptive or correlated with an adaptive aspect. You write:
"self-harm is a byproduct of the adaptive nature of oppression. I believe that those who are being oppressed unconsciously inflict self-harm to advertise their oppression, to show that they are a part of the oppressive society. Therefore, as members of the "IN" group, in sociological parlance, makes them attractive to others- of the "IN" group, and therefore better able to pass their genes onto the next generation."
But it might, with equal plausibility, be argued that advertising your oppression by self-mutilation is very maladaptive, because a. you impair your capabilities for reproduction and survival, and b. you are making it clear that you belong to the group with the least status (i.e the group which is being oppressed) in your society. This is usually considered to be maladaptive, and in humans we see a general tendency to display as much apparent status, health and wealth as possible.
I would be curious to see whether self-mutilation rates are higher in oppressive or hierarchical societies. That would, in a way, support your hypothesis.
Greetings,
Eric