Is this, however, the same person who wrote Can the White Race Survive?, or is it just someone with the same name? The latter is possible--the author of The Ultimate Solution to the American Negro Problem was Edward Eggleston, a Virginian who only had the same name as an author from Indiana.
This page suggests that Sayers was an author beyond just Can the White Race Survive?, writing under the pseudonyms Denver Bardwell and Dan James. Assuming this is correct--and I don't know either way--that would make him an author. But what about Esperantist?
There certainly was a fervent proponent of Esperanto by the name of James Denson Sayers around the same time. And it was almost certainly the author of Can the White Race Survive?, when you look at this excerpt from his chapter on the Jews:
I once heard an interesting series of lectures, the theme of which was to show that the three greatest men of all time were Jews: Jesus Christ, Karl Marx, and Ludwig L. Zamenhof.
Right now, some of you may be going "Who?" Zamenhof was the creator of Esperanto. I'm always tickled reading that sentence: the three greatest men of all time were Jesus, Marx, and some guy no-one remembers.
Anywho, Sayers continues:
One did not have to be a Christian, Socialist nor Esperantist to be profoundly interested by the reasoning of the speaker, who went on to outline an ideal, hypothetical world in which the teachings of Christ, the social readjustments proposed by Marx, and the neutral, simplified world language of Zamenhof were applied by the best brains of the world. A happy brotherhood of mankind was attained, in which the more fortunately endowed of intellect used their natural gifts for the common good instead of for selfish superiority. He stressed the important fact that those three Jews did their life-work without expectation of material reward and died in sacrifice for their principles.