Why (if anything) is a planet clearing its neighborhood important?

[Aedilred]

My (utterly layman's) understanding is, basically, that precision requires some sort of definition, which planets more or less didn't have. It was a "This is a significant celestial body", without having a clear idea of what made it significant.

Eris was discovered in 2005. Because it is bigger than Pluto (about a quarter more massive), the argument went "Well, if Pluto is a planet, then so is Eris". Which led to the discussion of "Well, what IS a planet? If Pluto is a planet based on size, so should Eris be. But then what about Ceres and the larger objects in the mid-system asteroid field?"

So, they sat down and hammered out a definition. That definition excluded Pluto, Ceres, Eris, and other "dwarf planets" more or less because it did. I'd wager "We need something resembling a manageable number of planets" was part of it, but I'm not sure.

I think it is the height of oddity to assume that people who, on the completion of their schooling, opted to take an additional 6-10 years of optional schooling, and then actively choose careers in the same field as their optional extra decade of schooling, chose a definition on something directly related to their field and would be globally publicized, solely or even partly to avoid memorizing a short list. Memorization which is almost certainly not required by anyone past sixth grade anyway.

I have been told by an astronomer - albeit one who was not present at the conference, being at the time too junior - that "keeping the number of planets manageable" was indeed one of the principal reasons for shrinking rather than expanding the list. But, as Peelee surmises, this is not for the benefit of astronomers, or at least not directly. Rather, it was to keep the number manageable for the public. From what I understand, from an initial list of nine that could no longer be justified on any scientific grounds, they were faced with a choice between reducing that to eight or expanding it to probably somewhere in the region of thirty. There was no particularly compelling scientific reason to choose one over another.

The view taken was that the average person with no particular interest in astronomy can be taught and easily remember a list of eight (or nine), but a list of thirty-odd would be too demanding, with the result that fewer people would bother to learn/remember the names of any of the planets at all. This was likely to lead to a decrease in public understanding of and interest in astronomy and its related fields, which is bad for the public and bad for astronomy. So Pluto was sacrificed for the greater good.

What I don't really understand is why so many people still seem to be put out over a decision about technical definitions that happened 16 years ago.