You know, I spent 20 years of my life in the service of this country by serving in the U.S. Navy from 1982 until 2002 when I retired.
Free speech is one of those rights that we enjoy, and because of our system of government as well as the fact that the military is willing to defend this country and all of the rights it has, I have no problem with him sitting down.
It's his right under free speech. If he believes that there is an issue that needs attention, and he's willing to be peaceful in his demonstration of his support for said issue, then let him. You as an American citizen have the right to comment on his free speech and can let him know how you feel.
However....................you cannot stop him, just as he cannot stop you from expressing your opinion. I personally support his right to demonstrate peacefully as he sees fit.
As far as the gymnast who didn't put her hand over her heart? Give the girl a break.............she stated that she grew up in a military family and that she was taught to stand at attention whenever the national anthem played. I can understand that, because many military people that I have served with did the same thing. If they were in uniform, they stood at attention, and did the same thing in civilian clothes. The only difference between civilian clothes and uniform was that if they were in civilian clothes and had a hat on, they removed it and stood at attention.
Just another example of people bitching about others who they know are better than them, so they think that by picking at one little detail, they can feel superior to them.
Unfortunately, the people bitching about the athletes could never reach their stature in competition if their lives depended on it.