If I were a professional athlete (I know, use your imagination) and, let's say, my team were going to play athletes from Iran or Cuba and China - nations with which I have a lot of disagreements - and the national anthems of those nations were played, despite all of those disagreements, I would stand.
Basic courtesy. Traditional courtesy. Doesn't mean there haven't been historical wrongs. Is not an endorsement of current policies. It is basic courtesy.
Don't lawyerize everything. Don't politicize everything.
Basic courtesy goes a very long way.