The National Anthem, like the American Flag, like the Pledge of Allegiance, are symbols of this Country: disrespecting them is disrespecting this Country.
How is the kneeling disrespectful? Because people are asked to stand and they know the reason is to show respect. That question shouldn't even be asked.
Protesting is an American Right - an important one, but doing it in a disrespectful manner should not be tolerated. Players have plenty of time and plenty of available platforms to protest if they really want to, but heck, they can't even agree on what they are protesting.
What also bothers me about it is the players saying the NFL can't stop them. They are on-the-clock as NFL employees, on World-wide media, acting as representatives of the NFL - the NFL can, and should stop them.