NFL players certainly have the right to protest, to be activists, to fight for others. But I think many people tune into the games to forget their problems, to escape the world, to have fun.
This crashes two worlds together. I'm sure there are some people that would rather watch a mindless action flick, or a game show, or an unscripted reality TV program that just lets them vegitate, rather than be reminded of all the troubles of the world.
Just my opinion. Personally, I don't watch the national anthem. I tune in right as the kick's in the air usually.