I recall your e-mail query back when and I definitely recall sending an answer. I don't remember exactly the way i put it a decade ago but that capitalization policy - widespread on the left - followed the longstanding left tradition of capitalizing names of either oppressed nations, nationalities or groups of people that have/had nationality aspects even if primarily defined by other characteristics ("racial" characteristics, ethnicity etc.) For instance: Chicano/a, Native American, and African American or Black, all capitalized (as was Negro in an earlier generation on the left). Generally, left publications also capitalized terms that were explicitly nationality-related when referring to white folks - for example, Anglo, used in certain contexts to distinguish from Latino or Chicano or Mexican-American. But the term white, since it was defined historically in purely racial terms - in fact, racist terms, via the rule that "a drop of african blood" makes one not white - therefore was not capitalized; capitalization was/is seen as a negative concession to white supremacy, to the idea that there is in fact such a thing as a "pure white" nationality.