NASA wasn’t the one who made the decision that Pluto wasn’t a planet. It was the International Astronomical Union.
Also if you count Pluto as a planet, then, according to current knowledge, it is highly likely that there are about two dozen more candidates for ‘planets’ in our solar system. And estimates based on objects that need more study place the number of dwarf planets like Pluto at over 200. Far too many for the average person to be expected to memorize in school. Shouldn’t there be a way to separate them into smaller groups? Well there is.
There are regular planets. Which orbit the sun, are spherical (or ellipsoid) as a result of their own gravity, and are massive enough to have cleared (or ‘swallowed up’) all of the debris within their orbit. Even a planet as small as mercury makes up well over 99% of the material in it’s orbit.
And then there are Dwarf planets, which have the other two criterion but are so miniscule that they themselves only make up a fraction of the matter in their orbit. Such planets are Pluto, Ceres (which is as close to us as the asteroid belt between Mars and Jupiter), Eris (which is actually larger than Pluto), Haumea, and Makemake.
Lastly there are asteroids, which have a large mass, but are not ellipsoid as a result of their own gravity.
The object on the left in this picture is Vesta, a large asteroid. In the center is Ceres, and earth’s moon for comparison on the right.
The only real dispute about Pluto is that the definition of ‘Dwarf Planet’ does not indicate a percentage of material in the orbit that needs to be comprised of the planet itself in order for the orbit to be considered “cleared” by that planet. If we are going to study other solar systems in the future, then we need to have more specific definitions in order to classify celestial bodies.
When you classify things based on their properties, it makes science a whole lot easier. Do people object to the taxonomy of plants and animals? No. Because without that classification system studying living things would be much more difficult. If we are to one day know of as many celestial bodies as there are species on this planet then we need a classification system that will help us study them.