I have many issues with the way my country treats people here and abroad. The fact that we can criticize the country legally and in public is, in fact, one of the benefits of not living in a fascist state. I, and many others, fear that America may go down the path towards fascism, as many once-democratic societies have.
What does going down the path towards fascism look like? Well, it starts with asserting the sanctity of the flag, anthem, and national leaders, along with religious-style worship of those three. Then, criticism of the deified leaders is squelched and later made illegal. Dissidents are rounded up and arrested, and supporters are elevated and empowered.
Playing the anthem alone isn't fascist, but it is nationalistic. It's a political act. Protesting nationalism is also a political act. If you'd like the football pre-game to not be politicized, you have to start with not politicizing it by playing the anthem and requiring the players to stand on the field and participate in the nationalistic display.
Suggesting that protestors of nationalism should be fired, arrested, or leave the country is fascist. I might ask you, if protest bothers you so much, "how can you possibly stand living in a country" where the very first amendment in the Bill of Rights asserts, "the right of the people peaceably to...petition the Government for a redress of grievances"?