Using a proper name for the body of water between the Korean peninsula and the Japanese archipelago is not simply a question of changing the name of a geographical feature. It is part of the national effort by the Korean people to erase the legacy of Japanese Imperialism and to redress the unfairness that has resulted from it.
It is an absolute mistake to hear just one side of the story and to blindly follow. If we leave these kinds of things alone, it causes serious problems that disturb the order of international society.
For your reference, Dorling & Kindersley, one of biggest textbook publishers, worldatlas.com, one of prominent online map provider, and one of the biggest mapmakers, National Geographic have already corrected their errors after we pointed out their errors. They are now using the correct name, "East Sea".