That's not my commentary, that's the title of the article. I think the author explained his assessment well.
But I'll try to add my own opinion.
No one questions the strategic value of Greenland.
It was beyond foolish for Trump to have
portrayed the idea as a "real estate deal" and to have characterized Greenland not as an asset, but as a liability that "hurts Denmark very badly". He acted as if we'd be doing Denmark a favor to take it off their hands. That was some clumsy swagger.
What was idiotic was how he handled the Danish Prime Minister's rejection. As explained in the article, Denmark is not only a reliable NATO ally, it is among the US'
"9-Eyes" countries who share intelligence against common enemies, and it permits a large US military base of huge strategic importance on Greenland [[they said no both to Russia and to China when they asked for the same).
Like an insolent child unable to accept his flirtations were rejected, he
had a tantrum and stormed off, kicking the dirt along the way. Hardly a way to treat a Queen, especially one that is a proven ally. His ego was hurt, and that's all that matters to him, so he put everything else at risk.
He even had the nerve to pout how the Danish prime minister is "nasty" and didn't treat him nicely. That comes from a man who can't go a day without gleefully hurling personal insults on Twitter, before the cameras, and in person. He has no self-awareness.
Immoral? I wouldn't go that far this time. But he has given us countless other examples of that.
Yes, Greenland is very strategically important. Trump just massively F'd that up.