Why do people weigh oppression and rank it contextually? (ex. Tropic Thunder)

People weigh oppression because we see our side first and another person's side of the issue is secondary in your subconcious. For instance to me, racism and ism are at the front of my mind before the issues facing the mentally disabled because I am not aware of those issues. Because people are ignorant of how other people are oppressed, they are more likely to believe that the oppression they've encountered should be more offensive when displayed than oppression that faces other people. For instance, which is more offensive to me, a black woman, c**t or the n-word? Aren't they both words that have signified the oppression of two of the social groups I was born into? Why would I rank them? Etc. Etc. It all boils down to the way we tend to group ourselves.