1. "Adjective nouns" need to have similarity to "noun" but aren't necessarily a subset. Gummy bears aren't a subset of bears either.
Gummy bears are not a scientific term. Besides, the IAU itself already uses the word dwarf in this manner. Dwarf stars, dwarf galaxies... but carved out an inexplicable exception for dwarf planets.
I'd like to see a citation on this. I highly doubt that you can simulate the formation of a solar system where multiple Mars analogues can coexist in the same orbit
False equivalency. There's a difference between "two Mars sized planets existing in the same orbit" and "Mars' orbit having been cleared". And more to the point, the biggest problem with the concept of Mars clearing its orbit is that its orbit was already largely cleared when it formed. According to our best models, Jupiter reached all the way in to around where Mars' orbit is today, and had cleared almost everything to around 1 AU. Earth and Venus accreted from planetesimals between each other. Mars accreted from planetary embryos ejected to the space in-between Earth and Jupiter. Without Jupiter's migration, simulations produce an Earth-sized Mars and several planetary embryos in the asteroid belt on eccentric / high inclination orbits, something akin to the situation between Neptune and Pluto - except with the embryos nearly Mars-sized.
3. In a geological sense yes. But the current definition of planets is based on orbital mechanics, after which Earth is a lot closer to Jupiter than to Ceres/Pluto.
Huh? By what aspect of orbital mechanics? By semimajor axis and velocity, Earth is much closer to Ceres than Jupiter. Are you talking inclination and eccentricity? Then we should boot Mars in favour of low inclination / eccentricity asteroids.
4. Hydro-static equilibrium as a dividing line is way worse. There are roughly 100 TNOs where we don't really know whether they are elliptical.
Hydrostatic equilibrium can be very easily estimated based on mass, which can be approximately deduced within a range of feasible albedos and densities, and very accurately deduced if the body has a moon. By contrast, it's almost impossible to estimate neighborhood clearing to any distance beyond Neptune, or at all in the case of extrasolar planets. Which, to reiterate, the IAU definition says aren't planets, even though they have an extrasolar planet working group.
We'd have to visit each and every one of them with a probe just to put them in the proper category.
This is utter nonsense.
Meanwhile, it's completely clear which bodies qualify for the "clearing its orbit" rule.
No, it's not. We have virtually no clue what lies in the outer reach of our solar system. As we speak there's a search for a new planet that could be as big as an ice giant. It's a huge open question as to whether it would have cleared its neighborhood, and it will be very difficult to ascertain.
All currently qualifying planets have roughly 99% or more of the mass in their orbit in themselves. Ceres has 30%.
You seem to have some weird concept going on that "semimajor axis = orbit". Ceres has nothing of significance in its orbit. The asteroids are not all in the same orbit. They're certainly more likely to cross each others orbits, but that's not the same thing.
And again, since you apparently missed it: the reason that the inner solar system is largely cleared except for the asteroid belt (and the reason that the latter exists) is Jupiter. Mars did not clear its own neighborhood.
5. The definition should be mutable. Why should a planet that gets ejected keep counting as a planet?
You seriously have to ask why something that hasn't changed but is in a different location shouldn't suddenly be declared to be something entirely different? If you take a rabbit to Canada does it suddenly become a dwarf rabbit?
6. I highly doubt life could form in a non-cleared orbit.
Once again, you're stuck on this misconception that the only orbital parameter that exists is the semimajor axis. And also apparently a notion that stable orbital resonances don't exist.
Orbits can come in a wide range of forms. If you want to see how crazy they get, check out Epimetheus and Janus ;)
As for a life bearing celestial in orbit around another (gas giant) planet: I don't think anybody feels bad about calling that one a moon? As in "Yavin 4".
The funny point with your example being, that whenever you illustrate a large round (hydrostatic equilibrium) moon in sci-fi - Star Wars, Star Trek, Avatar, whatever - people invariably keep calling it a planet and having to correct themselves. We inherently recognize "large, round object with relevant gravity = planet", and have to shoehorn our minds into not using that term.
7. "Within each other's periapsis and apoapsis" seems like a reasonable enough definition that neither Ceres nor Pluto qualify for.
Once again, you ignore most orbital elements (seriously, stop right now and go read the Wikipedia article on orbital elements). We don't live in a 2D solar system. And your notion is oversimplified even for 2D.
All of this, let alone other aspects such as mass ratios, resonance, metastability, etc. And it gets even more complicated when you view the solar system not as a 2-body problem but a multi-body problem. Then things like horseshoe orbits, Lagrangian points, etc come into play.
8. Yes that's silly but that'll probably be changed easily enough and has no effect on Pluto.
1) It's over a decade later. Where's the fix?
2) It's just a symptom of how horribly hasty and ill-thought-out their action was.
9. How are you planning to ascertain hydro-static equilibrium for an exoplanet if we can't even do it for Varuna.
What are you talking about? Varuna is the size of Ceres. The fact that it hasn't been declared a dwarf planet by the IAU is again a symptom of the IAU's dysfunction on this issue. See #18. By contrast, we'd have no snowball's chance in hell of identifying all potential orbit crossers for it.
The fact that you bring up Varuna makes me think that you feel it shouldn't be a planet because it's an oblate spheroid. If so, that just reveals yet another problem with your understanding: you need to go look up the definition of hydrostatic equilibrium. Hint: if Varuna wasn't an oblate spheroid, then it wouldn't be in hydrostatic equilibrium.