I guess I can see that taking a knee during some ceremonies involving the flag and national anthem are off limits, but this is a fake patriotic display put on by the NFL, a game played by adults, to make more money - it's marketing, a money making ploy. If they made more money not putting on the anthem, they'd end it tomorrow. For years they were in fact paid by the feds to put on these displays - "we'll pay you $millions to do more fake displays of patriotism."
So I guess I just cannot get upset about some player kneeling for THAT event. Or at least I don't get any more upset about that than I do about people in the stadium who are in line to buy beer and hotdogs and peanuts, or who are still in the parking lot, or who play with their phones during it, or are taking a last bathroom break at home before the game starts on TV, or finishing up some nachos and getting beers for everyone.
If this was a funeral for a soldier killed in combat, OK, I agree, don't ever take a knee. But this is an NFL game for goodness sake....