Once something has become an accepted way to respect their sacrifice to use it as a statement is offensive. That is exactly what he is intending it to be. If he would say that he feels that sitting is a better way to show respect people wouldn't care and would dismiss him as a kook.
Let us say that he has a good point about police brutality. It is still not something which the country stands for. If it exists as they claim it would be an issue which everyone would agree needs to be fixed. The symbolism of the flag is what is allowing him to be earning millions a year instead of working on a tobacco field. With his actions he is turning his back on all this country gave him.
Any reasonable person will realize that bigotry exists. Many of us have experienced it. But if a Jew would disrespect the country which has given more freedom than any other in thousands of years due to some bias against him he should be condemned.
So many thungs wrong with what you wrote.
So one by one.
1. The national anthem isn't an anthem to respect the dead. It is used when respecting the dead, but when they DON'T say "let's sing this anthem in honor of our troops/vets", it has nothing to do with them but rather America and everything it represents. Yes that includes the troops, but that also includes all the bad things along with it. Obviously if the anthem is recited in memory he is disrespecting those that sacrificed for him. Though it doesn't help that the NFL and other sports leagues are literally paid millions to respect the troops, if you ask me that's worse than sitting down during a random non-troop supporting anthem.
2. America has had a problem with police brutality and has done nothing to reel it in. The brutality stems from policies in place that promote cops to use bullets first and policies that say the cop is never guilty no matter how wrong he is. Cops rarely ever get convicted and that's policy. You want to say this flag represents America, you can't change the facts, America is comprised of xyz mostly good things but also bad things.
3. You're obviously a firm believer in american exceptionalis as you believe an athlete like him wouldn't get paid millions to play sports in other countries. Yep only in America. FYI soccer players worldwide aren't picking tobbaco, they are some of the highest paid athletes in the world.
4. Criticizing a countries policies isn't akin to disrespect. We live in a democracy where the beauty of it is that citizens desires can actually be passed into law. Protesting a policy is part of the democratic process, and might be more patriotic than anything you've ever done.