When I first heard about it, I thought it was stupid. Pluto has been a planet since before I was in elementary school - why change it?
But once I understood why it was done, it made sense. As telescopes got better, astronomers began finding other objects roughly the same size as Pluto, or even bigger, orbiting the sun. If Pluto is a planet, then these other objects are, as well. Either the solar system would have an ever-increasing number of planets, or objects of that type would have to be reclassified.
Don't be sad for Pluto. It may not be a planet anymore, but it turns out it has lots of friends out there at the edge of the solar system.