During the slave era, white slave owners believed they were doing good for the black man. That this was their optimal role in society.
If you are not the oppressed, you cannot objectively be part of the discussion about whether or not and how the oppressed are being oppressed. It's quite simple. The only thing you can do is help. If you argue against their oppression, you are perpetuating the structural inequality.
You can be oppressed and be an oppressor. There's something to be said for how and why, but weighing them against each other is nebulous. This has been true throughout history. re: israel-palestinian, hmong-vienamese, english-scottish, etc.
> If you are not the oppressed, you cannot objectively be part of the discussion about _whether or not_ ...
I don't find this assertion is sound. There's an element of ideology in there, which I appreciate, but I do not agree on this practical tenet. If it was rephrased or attenuated to a more specific decisioning system (ie the latter part of the statement, is more palatable, albeit also something I don't fully agree to), I would re-examine it.