Oh and for the record: Stern calls Pluto a planet, and makes some very good arguments.
And I'll add more that he doesn't make (though his are best!): it's ridiculous to call something a "dwarf X" and then say that that doesn't count as an "X". In any other field of science, if you had an "adjective-noun", it would also be classified as a "noun". If you have a dwarf shrew, it's also a shrew. If you have a dwarf fern, it's also a fern. Heck, even in the same field, astronomy, the same rule applies - a dwarf star is also a star.
Under the IAU definition, extrasolar planets aren't planets either. They don't even have a name - they're not anything at all. Not like we'd be able to classify them under the definition without dispatching a spacecraft all the way to each different star system even if they weren't excluded. The IAU definition also claims that they will create a system to establish more dwarf planets - something that clearly has not been done. There hasn't been a new dwarf planet accepted in nearly a decade, despite the fact that we know the sizes of many of them better than already-accepted candidates were known at the time. Quaoar is much bigger than Ceres, and we know it's size down to a mere 5 kilometers margin of error, yet it's not a dwarf planet. The IAU not only made up their ridiculous definition, but they're not even upholding it.
As with pretty much every categorization of object in pretty much every field of science, you need heirarchies and multiple groupings to describe the world. Among planets, we already know of significant diversity, and should only expect it to grow - hence we have terrestrial planets, gas giants, ice giants, hot jupiters, super earths, etc, and yes, dwarf planets - which should be just another category among the significant diversity already out there. Everyone knows a planet when they see it - you don't have to scan its orbit to see if it's "cleared" it, with some still-not-yet-agreed-upon definition of "cleared". If it's large enough to relax into a hydrostatic equilibrium, that's both meaningful, intuitive, and what people expect when they hear the word "planet". By any reasonable definition, our solar system has at least dozens, potentially hundreds of planets. And that should be seen as something to celebrate, not to be appalled about.