This book isn’t a traditional story of good versus evil. We meet a variety of characters, many of whom have both positive and negative traits. (For example, the prince’s flower is both egotistical and loving.)
However, over and over in this book, the narrator keeps pointing to a group of people who don’t see the world in the right way. This group doesn’t have “true understanding” (1.10). They don’t get the narrator’s Drawing Number One, and they wouldn’t understand that there’s a sheep inside the box he draws. In fact, if you gave these people a copy of The Little Prince, they probably wouldn’t get the book.
They are grown-ups. They think they are important and they are obsessed with “matters of consequence” (15.37). But thinking about that consequence blinds them to what is really “essential” (21.36). And, in a story that’s all about learning to see things truly, what could be more antagonistic than that?