should:Pluto was known as a planet for 75 years. This means that most people already knew it as a planet, and would be extremely confused. All of the books about planets would be inaccurate and changed. Not all people can access brand new books, leading to inaccurate information.
shouldn't: The same reason that it was unclassified as a planet. It does not adhere to all of the rules of being a planet. It is not completely round and does not have a round orbit around the sun. Pluto does not have every requirement to be a real planet, and therefor, it would be incorrect to have it classified wrongly.
