I am a veteran of the Gulf War so for me, the song stirs strong emotions. What better way to begin a sporting event than to hear the National Anthem played and celebrated by tens of thousands of people. The flyovers and parachute drops are nice, but for me, it is the song and the emotion that it stirs in an 80K fan filled stadium that gets me fired up.
If someone feels strongly in not participating, it is certainly their prerogative, but I feel it is disrespectful not to at least stand in observance.
I may not agree with the politics of places like North Korea, Iran, Syria, etc., but if their anthem were played in an Olympic venue, I would stand out of respect.