I've seen themes and elements from Dr. Seuss's Horton Hears a Who applied to a variety of things, such as the abortion debate, dwarfism awareness, and space aliens. While I can see how they could apply to these topics, none of them seem likely to be was Dr. Seuss was intending to talk about. But the book, like many of the author's other works, is apparently meant to convey a message.
What message was Dr. Seuss intending to express in Horton Hears a Who?
The reason he wrote it is very interesting. He thought of the "person's a person, no matter how small" from his experiences in post-war Japan. He had drawn anti-Japanese cartoons during the war, and he realizes this: [from an interview here]
Well, Japan was just emerging, the people were voting for the first time, running their own lives—and the theme was obvious: “A person’s a person no matter how small,” though I don’t know how I ended up using elephants. And of course when the little boy stands up and yells “Yop!” and saves the whole place, that’s my statement about voting—everyone counts. It’s all left over from my war experience, when I was making propaganda and indoctrination films. One of them was to encourage soldiers to vote.
So the entire thing is an allegory for post-war Japan. The kangaroos, therefore, represents Americans and the Whos are the Japanese. The slogan "a person's a person, no matter how small" is really what Seuss is trying to get at.
On the other hand, he also said this on the same site:
Parenting: Do you use propagandistic skills in your books?
Seuss: of course. However, most of my books don’t carry heavy morals. The morals sneak in, as they do in all drama.
As you both know, Geisel tended to have a major theme and then secondary them (eg - Lorax with climate change/environment and proactive involvement). A number of authors comment on this, but the primary is certainly "a person's a person" and that seem to definitively be the plight of the Japanese during/after WWII. The secondary theme was holding onto beliefs you strongly believe are true (with data and evidence vs anecdotes and twitter/facebook/truthsocial - i.e., BS) and fighting for them regardless of the resistance you encounter.
