3) They were worried there might be more planets than they can count on their fingers and toes.

Just as the evocative phrase "Big Bang" was invented as an insult (by Fred Hoyle?) but came to express the quintessential essence of the point-of-unimaginable-energy-density-in-a-fiery-explosion-billions-of-years-ago theory of the origin of the Universe, so I think you have struck the nail on the head here.

Humans are classifiers and counters by nature. But we distinguish the counting and naming of meaningful things from the counting and naming of meaningless things.

Look at the Seven Wonders of the ancient world; or the way we award GOld, Silver, and Bronze Medals in sport; or one of Letterman's "Top Ten reasons for...." (Or your own conscious or unconscious use of a "top ten" for your mocking reasons why Pluto should still be a planet). People like numbers they can easily grasp in their head.

In contrast, look at the list of dumb and dumber names for Asteroids or the difficulty of grasping star names, numbers, locations in space, and physical properties. These are for stamp collectors and train spotters.

We have catalogues where everything is written down and these are consulted for reference and mied for statistical analysis, but when you want to think of things, you look for groups that can be understood simply and rapidly.

The reality of Pluto is that even now, an honest and open planetary definition that admitted any self-gravitating spheroidal object, would introduce an extra half-dozen worlds to our planetary Pantheon. And that number is ALREADY too many, let alone the observation that we will in the next few decades discover dozens to hundreds more of KBO's that will qualify for minor planet status.

I'm a simple person at times, and I don't need to know right now the names of all the beetles that live amongst the roots of a certain species of tree. (Specialist entomologists can do this for their Ph.D. dissertation, and I can look it up if I ever need to know it). Similarly, I don't ned to know ON A DAILY BASIS, the name and size of every known moon, asteroid, and KBO, or even the subset of larger ones. And I'm a planetary scientist to whom these things ARE relevant.

Sure, I need to know where to get the list from, so that I can ground-truth models of planetary formation, for instance, but neither I nor, especially, the man in the street, needs to know this and hold it as a key fact in their head.

It doesn't really matter whether Pluto remains a planet or not. What DOES matter, and is the REAL issue here is that we stop RIGHT NOW in naming new worlds as planets because we've already got enough.*

Once we decide to stop letting new ones in (unless we unexpectedly find another gas giant or something entirely wierd and huge out there), then the same logic that you are using to insist that Pluto MUST be a planet turns round and says that Pluto MUST NOT be a planet, if the new ones can't be.

This is Mike Brown's unspoken and perhaps even unthought argument. It's belated recognition that Clyde Tombaugh was wrong. He did NOT discover a planet. The orbital predictions he used were wrong, but he accidentally (serendipitously for him) discovered a maverick KBO wandering in one of the places he wrongly looked in. SImilarly, Mike Brown has NOT discovered a handful to a basketful of planets, he has observed a bunch of ice balls out in the Kuiper Belt. None of these is remarkable, but some are larger than Pluto. Ergo, Pluto is not particularly remarkable, either.

Sorry Clyde, sorry Mark, and sorry Mike. Pluto isn't a planet, Xena isn't, Quaor and Varuna aren't. Sorry to Piazzi, too, Ceres is not a planet, either...

* Footnote - is it appropriate in science to say "Enough and no more!"?

In the long term it isn't. Science is an observational philosophy. We observe the universe and try to explain it, then make new observations. As our observations improve and our chain of inference grows, we learn more but must always be prepared to cast aside even solid foundations when our learning outgrows them

So it is clearly forseeable that IF we discover a new massive object in the Kuiper Belt or beyond it that is gravitationally bound to our Sun, then it will become defined as another planet.

But this does NOT mean that we should allow minor icy or rock bodies to share the "top ten" of Solar orbiting objects with other entities that clearly outrank them.

I'm sure the exact definition of "planet" will change and mutate as it evolves, but the underlying REQUIREMENT is that there should be no more major planets than joe and jane public** can comfortably hold in their head, at the same time as they are watching TV, or whatever the future brings in the way of mass media...

** And with respect to Joe and Jane Public, also no more planets than non-planetary specialists can comfortably hold in their head while they conduct their own (related or unrelated) speciality.