In the various conservative media pieces on anti-American behaviors by NFL players and teams, there is inevitably a mention that the actions of the players fall under Freedom of Speech.
That's certainly true.
It is not a crime not to stand for the Anthem. Our government doesn't compel people to stand for the Anthem, the way that it compels them into certain other kinds of speech that fit a left-wing agenda. (Just ask the photographer who shows no interest in participating in a gay wedding.)
America does not command or compel anyone to be Americans.
So let's define what we're talking about here.
If you don't want to stand for the Anthem or be an American, you don't have to be. Naturalized citizens take an oath to "bear true faith and allegiance" to the United States and its Constitution. For the native born, the oath is assumed.
But it is a requirement.
Unlike Cuba or China, America doesn't compel allegiance. But allegiance is required. It's possible to live in the United States and not be a citizen. It is also possible to leave America.
But for Americans, allegiance is not an option.