The problem with such statements is that they are inherently defeatist attitudes that only breed complacency and apathy, as if you're right, then what the hell is the point of trying to organize within nations such as the United States. Further how do you classify who is a settler in a state such as the modern day United States? Do you lock mixed race people out of the movement as well? How about if they are white passing? Or how about recent "white immigrants"? What about the millions of white appearing people descended from settlers that live in abject poverty or are crushed under the oppression of capitalism? You can't seriously believe that there's absolutely no way such people could be mobilized or organized to join or lead a revolution, can you?
In such a racially and ethnically diverse nation like the United States, do you genuinely believe that you will ever effectively mobilize the working class if you limit your demographics to... who exactly? "Pure" Native Americans and "pure" black individuals who can trace their roots back to slavery and have no race mixing in their lineage?
I also fail to see the issue with the article, the author agrees that the United States is a settler colonial project, and that the lasting consequences of this must be addressed within a socialist society. However, all he states is that chasing bizarre notions of racial purity when organizing only sets back the movement by isolating elements of the working class that are ripe for education and radicalization. What do you see wrong with his statements?
Ok, lets say you're right and are able to effectively exclude who you label settlers. Ok... what now? How does this benefit your organizing, popularity among the proletariat, and ability to sway the population to your side?