The "big" deal is that a ton of celestial bodies of comparable size to pluto would have to be considered either as planets or as general debris. Finding a clear definition which would include pluto as a planet and not include other stuff would be very impractical and possibly nearly impossible.
But the biggest fuck up was to name a non-planet a "dwarf planet".
I'm well aware of the existence of countless dwarf planets in the solar system, and the naming issues that arose from the discovery.
I don't mind that they called them dwarf planets. But I don't know why everyone got so upset about it. It sounds like just another class of planet to me, which seems quite appropriate.
I agree that they marketed the change about as poorly as they could.
Sure, people have taken the matter way too personal. That's mostly people who have a nostalgic relationship to their childhood classes about "the 9 planets".
As I've read, they made the definition in the particular way to remove gray areas of inaccurate meassurements. A celestial body shouldn't be wrongly classified due to being a few kilometres larger than some limit, then be reclassified later due to better meassurements. Planets need to be somewhat spherical, orbit a star and clear their orbit from significant debris. They made a great system which doesn't leave big gray areas. A planet is defined in a well thought out way by people way smarter than me.
And then they go and call the non-planets "dwarf planets".
The deal is the weird part where they made a specific point of and big deal out of the new classification not being a type of planet despite having the word planet in the name.