First of all, he points out that Esperanto is much more beautiful than the Black Speech. "Just consider the word Esperanto," he writes. It is euphonious and has two e's and one o: In the Black Speech, e does not exist and o is rare. He quotes the poet Kálocsay concerning L. L. Zamenhof, the inventor of Esperanto: "He did not create poetry with Esperanto, but Esperanto with poetry."
But more serious is the fact that Esperanto was constructed for noble purposes, while Sauron made the Black Speech only to further his evil plans. Bojesen writes, "The Black Speech was made to spread death and hate. Zamenhof created Esperanto for peace and love."
Of course, I agree that Esperanto with its "Italian" flavour is much more beautiful than the Black Speech. I am also aware that Esperanto was constructed for a much more noble purpose than Sauron's reason for making the Black Speech. Zamenhof wanted to make it possible for the peoples of the world to understand one another. Sauron made the Black Speech to replace the existing tongues of the different tribes of Orcs because it was easier for him to rule them if they spoke just one language. Of course, I don't claim that Zamenhof's noble purpose and Sauron's evil plans are comparable! I just used the word "Esperanto" in the most general sence - "simple, constructed interlanguage". Insulting the Esperantists was not my intention.
And now I'm just glad I didn't call Quenya "Tolkien's Klingon..."