Of course the US was founded on racism - and racism is a prevalent problem. You haven't read the argument fully and I'm not sure you've fully understood the discussion that Marley and I are having.
For Marley, the way to solve a problem like racism is to use identity politics - for me it is to use classic socialism. What Marley sees as the empowerment of BIPOC voices, I see as the setting up of ideological niches which will combat each other and detract from any real progress.
What Marley and I fundamentally disagree about is not that there is no racism. There is. We disagree about how to end it. Marley doesn't speak for all BIPOC, neither does any one person - it is an arbitrary grouping of skin colour that seems unified but really isn't. BIPOC are not a homogenous group and have no real consensus. When give every BIPOC equal weighting on how to interpret oppression - you end up discussing Bridgerton ad infinitum. This isn't about shutting up BIPOC its about elevating intelligent solutions.
My problem with Marley's general rhetoric should be apparent by race-flipping her articles. She speaks with high levels of race prejudice (perhaps quite rightly) and that makes her pieces very popular with certain demographics. She has an excellent call to action. It also means that she rarely offers a solution to the problem being outlined. Everything is about 'what they did' and 'they're oppressing' us - without really exploring that further.
Identity politics, the way that Marley uses it, is very compelling but I fear it splits the demos and moves everyone away from an actual real solution. The US population is made up of predominantly poor people, mostly white with a high percentage of BIPOC thrown in. Identity politics tells those people that middle-class BIPOC are 'more oppressed' than any white person. Whist that is semantically true - it very much undermines the lived experience of all of your working class. A perfect way to ensure they vote alt-right and no progress is being made.
That's the disagreement Marley and I have. Identity politics vs socialism. It's nothing to do with whether racism is a thing or not - such a supposition does not even feature in our debates.