Well, Colin Kaepernick's decision not to stand for the national anthem prior to his NFL games set off a storm of vitriol from American right-wingers. I can understand that many or most people don't agree with his decision, but that doesn't mean that his behavior is somehow off-the-charts in terms of actions responsible citizens might take. A little empathy on the part of white people, a little effort to see how life in the US might look to a person of color, including very successful ones, would help matters greatly. Instead of asking why Kaepernick did it we might wonder why it doesn't it happen more often.
This is not to say that anyone, white or black, has to or will agree with his analysis, but come on. When the Bundy gang seized a government building with the threat of deadly gun violence, conservatives fell all over themselves to champion them. Because they agreed with the Bundy gang, these law breakers were called patriots.
An interesting aspect of all this is that the Kaepernick they hate is a straw man. No, he doesn't think he is being personally oppressed. No, he doesn't need the publicity. Do you think someone would do as he did in the jingoistic world of the NFL if he were just being selfish? Here's a great article on this topic at Slate.
Oh, and when did standing for the anthem become solely about respecting our troops?