There were indeed "tons of anti-imperialists in Churchill's day" but the people you list (Marxists, progressives, Mark Twain.) were moral heroes who were ahead of their time. Churchill was a man of his time and place, born to a position of power and privilege who understandably bought into the system of white supremacy he was born into. That does not invalidate the heroic actions he took in the fight against Hitler. Wilson was worse than his time on racial issues, but that does not invalidate the heroic and visionary actions he took in forming the league of nations, or introducing the first American minimum wage laws.
I never once in this article, or anywhere else, ever said or thought that it was wrong to criticize Churchill or anyone else. What I said was that we MUST criticize our heroes, but that does not mean we should cancel or banish them because they deserve to be criticized.
I despise Reagan, who had no redeeming qualities in my opinion. His racism was real, but rather like Al Capone's income tax violations, is trivial in comparison to his other flaws.
John Wayne's muddle-headed comments about African-Americans and Native-Americans were no worse than most other people of his time. The comment about African-Americans could charitably be interpreted as a paraphrase of Booker T. Washington, but I'm not inclined to be charitable. His politics on other issues, especially his behavior during the McCarthy era, was much more unforgivable. Anyone who had problems with his racism would already have written him off for other reasons.