@freemo His arguments against “white moderates” are perfectly applicable to any other kind of political moderate though. Why do you think he only applied them to race politics? Plus, he wasn’t writing about “moderately racist people” – the letter was about people who, through a misguided vision of being moderate, kept insisting that his goals were just (so they weren’t really personally racists, just, as we would say today, insufficiently anti-racist), but the timing was wrong, a mantra that is oft repeated in many political contexts when some group wants change for the better.
Amusingly, I kinda agree that he was a moderate, since he only advocated democratic socialism, which is a moderate position from my perspective. It was, and continues to be, to the left of any of the US party positions though. He was also to the left of both parties on race, quite obviously. That’s why I vehemently disagree with calling him a “centrist” in the US context, although feel free to call him a moderate if you consider democratic socialism moderate.