I’ve always felt that, the moment you make something “sacred” and “unquestionable” you immediately corrupt it.
It’s definitely an impossible ask at least, especially when it’s an element of a democratic establishment (as opposed to say a religious object). If America stands for freedom, its people have the freedom to decide what the flag means to them, and in this case the flag represents a failure in that mission for freedom. In this way, people getting mad at those kneeling during the anthem are kinda helping prove their point.