It's not discussing wanting Greenland that is wrong, its threatening an ally about it through media instead of going about it in a diplomatic and friendly way. The motives also don't seem rational at all, but more about boosting Trumps ego and legacy. Trump obviously have an imperialism itch he is trying to scratch.
This is incredibly damaging for the USs reputation and alliance with the rest of the western world. A lot of European leaders are now one after one posting on X that Greenland belongs to Denmark.
Not excluding taking Greenland using military force would never have happened without Trump as president.