It is his constitutional right to express himself as he pleases.
But not standing for the National Anthem spits on all Americans. What a brain-dead low-life.
AS with most forms of protest....absolutely he has the right to do what he will, that includes accepting the consequences for his behavior. In the 60s people were fire hosed, beaten, spit upon, and killed just because they rode a bus or sat at a lunch counter. They were yelled at and cursed and vilified in horrible ways.
Poor Colin has to endure being booed