The real problem is...., we are making this a problem.
Should he stand? Absolutely. Does it "offend" me if he kneels. Sure. But he can express himself in any way he sees fit as long as he doesn't break any of our laws.
And while doing so, he can live with the consequences of his actions which means he isn't good enough for the baggage he will bring to any team. Even the Browns.
As for the protestors? Oy vey.