Mind you, when China became backwards rather than staying advance, it was Japan that was first to use the Chinese characters for new things that comes with modernation.
Should also be pointed out that for phonetics, Japanese still has hiragana and katakana where as PRC uses roman letters for pinyin.
It was also PRC that decided to move away from the traditional characters and evolved its language to more simple Chinese characters.
Yes, of course the Japanese understand the origin of Kanji. But the story isn't so simple.
So yes, it is just like how the roman letters have also been used and evolved along with the languages that use them such as German, French, English, etc. Also like how there is a family of languages that use the cyrillic script.
There is nothing wrong with it until someone like you uses langauge as a means to claim some sort of identity ownership. That is the only reason why it has gone hot here.