Some good points, but still not convincing. All NFL players have signed contracts knowing it was league practice for players to stand respectfully during the National Anthem before every game. The analogy of different coffee cup logos doesn’t apply. Besides that analogy trivializes the protest Colin is making.
You are right that in some sense a patriotic display could be considered political. But in the US sports arena context, it is an affirmation that the competition between different teams takes place within a larger national unity. It also acknowledges that the contest takes place in front of American fans. When playing outside the US, I could see the NFL have the players stand respectfully for the playing of the anthem of the host country.
Kaepernick’s protest invites other divisive protests into US sports arenas and threatens those arenas with more overt and strident political displays than they have ever experienced. But many American fans don’t want that. They are boycotting until the NFL fires Kaepernick. We didn’t pay to have our country insulted by a spoiled millionaire.