This is emotion driven sophistry leading to personal insult.
The question was who would define the oppressors
The answer is clear is that ultimately it's history.
It has nothing to do whatsoever about the legitimacy of the grievance of any group who as felt oppressed. To the extent they raise their voices often and loudly, they are likely to influence history so by all means they should do so.
A good example is the fact that history has pretty much concluded that the Confederacy was all about slavery and Southern slaveholders were oppressors. I don't take issue with the accuracy of this. My comment that at it's core it was about power doesn't in any way excuse the institution of slavery in the South. It was their way of establishing power. While abolition was a driving force behind the North's entry into war so was preservation of the Union and it sometimes amazes me that people who have no problem spying the sinister designs of capitalists in modern American, and indeed global, politics, don't imagine that it could possibly have existed relative to the Civil War.
Another example of clear and undeniable oppression is the Armenian Genocide carried out by Turkey beginning in 1915. While history recognizes the Turks were oppressors of the Armenians, the horrific massacres than led to upwards of 300,000 deaths are not widely known in this country. (Although I understand there is new film coming out that covers this period and so this may change)
In addition, while history notes that the institution of slavery has figured in human civilization for thousands of years, the empires and civilizations of the Chinese, Romans, Persians, Mongols, and the Greeks are not generally defined by the institution and no one is calling for removal of statutes honoring Aristotle who posited a theory of Natural Slavery.
Of course this in no way changes the nature of the Confederacy. It was what it was, but 500 years from now do you think the Civil War and slavery will be such a defining event for America?
The only substantial disagreement I've registered in this thread is with the proposition that every one in the South who wishes to honor their Confederate heritage is a bigot who just would love to see a return to the subjugation of African-Americans.
You can disagree of course, but I've lived in the South for 33 years and I've met many a Southerner who fell to romanticizing the antebellum South, and harbored a family heritage of resentment towards the North for the hardships the region underwent after the war. Some were bigots; most were not. I know you won't believe this but initially when I met someone like this I tried to argue that since the institution of slavery was the foundation of the antebellum South, romantic notions of gentility and such rang hollow. Eventually I gave up the argument because it tended to spoil dinner parties and backyard barbecues and if I didn't believe the people were bigots, I wanted to continue socializing with them.
To the extent these people could be faulted it was for their unwillingness to recognize how deeply African-Americans felt about Confederate symbols. They were selfish in the Southern conceit, but let him who is without sins cast the first stone.
Besides I eventually found that my energies were better directing at arguing with sanctimonious liberals, particularly if they lived in the North.
I grew up in the North and I know it was beset with racism and segregation (more entrenched than when I moved to NC in 1985), and the liberals in my neck of the woods who were full throated supporters of the Civil Rights movement (my parents for example) didn't want to do anything to break the color barrier in place within suburban NY communities for fear of losing property value.
No region of the country has a spotless record that might enable them to denigrate any other. A lot of very good and decent people having been living in the South for a long time and it is just calumny to suggest they've cornered the market on racism.