It’s been a LONG time since I’ve read Burroughs, but I don’t remember him as being anti-racist. From what I can recall he shared the mildly racist viewpoint that was the conventional wisdom of the day.
Lord Greystoke was a superior human being because he was descended from English aristocrats. He was a gentleman by instinct, presumably genetically transmitted.
Blacks were generally background only, as I recall. The whites were both the villains and the heroes. Russians and Frenchment, in particular, seemed to inherit villainy.
But it’s been a number of decades, so don’t quote me.
The descendants of a (noble) aristocracy is always, in a Burroughs story, the superior man to a nobody, or the product of a degraded and corrupt and tyrannical aristocracy.
Blacks in the Tarzan story could be beautiful or ugly, smart or stupid, noble or bestial.
In the most recent Tarzan book I read an Englishman found a lost valley of Crusaders, black as any African, but who spoke, dressed, and fought like Medieval English Knights. Besides mentioning their skin color at the beginning it was almost forgotten so much that by midway through the story I had to check to make sure he said their skin was black (he did). The Englishman (with the help of Tarzan) helps the noble black Crusaders against the villainous black Crusaders, and marries the black Crusader princess.
In that story there were Europeans, Africans and Arabs. There was a good European and a bad one. Good Africans and bad ones.Mostly bad Arabs, but a young Arab couple that was good and Tarzan saved and reunited the young lovers.
In fact the only “racist” statements I could find in the entire book were Tantor the elephant thinking to himself that “the white men were the worst” and the ‘good’ European explaining to the ‘bad’ European that their African porters were “like children”. Tarzan however did not treat them as children, and blamed them personally for leading ‘white men, helpless in the jungle without you’ into his territory.
Anyway, reread Tarzan or the Mars stories and you will get a different perspective.