Neil deGrasse Tyson is an astrophysicist and the director of the Hayden Planetarium at the American Museum of Natural History. In March he was interviewed on Point of Inquiry about his recent book, The Pluto Files: The Rise and Fall of America's Favorite Planet. The interview is available here. I haven't read the book, so my comments are based on the interview.
Tyson was indirectly involved in the change of Pluto's status as a planet to a dwarf planet. Back in the 1990's, the museum was re-building the astronomy section, and as he and his staff looked at the current science they decided that Pluto really had more properties in common with objects in the Kuiper belt than with the rest of the planets. Sparks began to fly when the New York Times ran a front-page story pointing out that in the display Pluto was not grouped with the other planets, nor was it referred to as a planet. The rest is history, with Pluto currently classified as a dwarf planet.
Tyson points out that the whole fight has been over nomenclature, not over the actual properties of Pluto, and he thinks that the reason for the attachment of many people to Pluto as a planet has to do with how we learn about the solar system in school. Rather than comparing and contrasting the objects in the solar system and discussing the process of discovery, the solar system is presented as a finished product with a mnemonic to help in memorization. This scheme becomes cemented in people's minds such that they feel a sense of betrayal when it is altered.
Science is exploratory, and as new discoveries are made we have to find or invent words to describe or label them. But often as discovery continues it becomes clear that the old system of labels is inadequate. As Tyson points out, originally planets were just lights in the sky that wandered relative to the other stars. As their capabilities grew, astronomers identified and named more and more wanderers until we reached nine, with Pluto as the last. But as astronomers learned more about Pluto, it became clear that it was rather different from the terrestrial planets (Mercury, Venus, Earth and Mars) and the gas giants (Jupiter, Saturn, Uranus, and Neptune), and they found that it was much like objects in the Kuiper belt (which was discovered in 1992(!)).
Ultimately, Tyson puts it this way: Pluto is not the last of the planets; it is the first of a new class of objects.
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