I served in color guards and honor guards throughout my navy career on base color guards, multi branch honor guards along side marines and airmen, the most prestigious of which was "The Admiral's Own" which was one in DC and we were assigned to perform at ceremonies the the Surgeon General of the Navy assigned us to (not to be confused with the Surgeon General of the U.S.). All that to say that I AM a subject matter expert, and I can tell you that their were MANY times we would do a rifle maneuver and end it by going to a knee for the National Anthem. The one I particularly remember was called the Queen Ann Salute, but there were others. SO, as a veteran, I have no problem with someone taking a knee during the National Anthem, its better than sitting.