Well at one time people "knew" that space was filled with Aether, and people knew that the universe was no more than 2 million years old.

But once you understand things more, some of the things you know turn out to be wrong.

In this case it's more like "we called this thing a planet before we knew just how tiny it really is but it's still cool so we now have categories for things just like it"

Which I think is neat.

You can be sad it's not a planet, we can also be happy that it pulled one over on all of humanity for such a long time.

Pour one out for Ceres, for being downmoted so long ago people forget it was a planet.

Pour one out for Makemake and Hamuhea, for being discovered so recently they never got to be planets.

That's messed up

the only thing that changed is what we call it, pluto has existed since before humans and will continue to exist after humans most likely, and it does not give even the tiniest shit about what we call it.

"planet" is an arbitrary category that mostly just exists because we like to put things into categories, much like the concept of a continent.

It's just really difficult to say that pluto is a planet if we want to have any sort of vague definition for what a planet is, because pluto is more similar to a ton of objects in the solar system than it is to the other bodies we very confidently refer to as planets.

If nothing else you have to also call ceres a planet if you include pluto, and how many people give a shit about ceres?