Tbf, it's kinda of bad for Messi to reject Spain.
It's his right but Spain is the country that helped him, give him money for treatment, provide citizenship for entire family and carefully developed him in their system.
It does leave a sour taste.
It goes deeper than that.
He left Argentina when he was 13.
Try to imagine yourself leaving your home, your school, your friends and your neighborhood to go all the way to the other side of the world on your own, without knowing a soul.
Any teenager would be devastated.
He always loved Argentina, iirc back in 2008 he wanted to represent Argentina at the Olympic Games and Barca initially wouldn't allow it, they even took the matter to court but Pep intervened and let him go.