Pluto Isn't Even A Planet?! What?!

[halfeye]

The thing is, planet is an arbitrary distinction. It always will be, no matter what they do. In this case, they chose an arbitrary distinction that was clearly defined, and almost entirely consistent with what had been done before. Unfortunately, they couldn't do both perfectly, so for lack of a better option, they chose to demote Pluto.
Any definition that would include Pluto and those many other objects wouldn't really have any benefit, other than simply including Pluto. It might not be the best reason ever, but for what is essentially a completely arbitrary decision, any reason is good enough.

Any reason is good enough?

The sky is blue so Pluto isn't a planet? The sky is green so Pluto isn't a planet? Today is Tuesday so Pluto isn't a planet? I don't agree that those would be at all close to good enough.

As I said above, I don't much care about whether Pluto is defined as a planet or not, though I think it's a shame they trashed so much history for the sake of pedantry, but the rule they made up to do it with is just silly. I totally understand the desire to have a metric that is independant of the particulars of the Earth and the Solar system, but while the metric they chose is independant of the Solar system, it totally fails to deal with potential other stellar systems in a reasonable way. At Pluto's orbit an Earth mass object would not be a planet by the metric chosen, and further out a Jupiter mass object would not be a planet by the same metric. We've probably already detected Jupiter mass minor planets by this silly definition.