"It's not how you treat a flag (or the anthem), it's how you treat Americans." (Sarah Kendzior)
They want to kneel to peacefully protest racial injustice, for the slain and the suffering. I am totally fine with that. The racial injustice that has been going on in St. Louis for instance is horrid.
By the way, players didn't start standing on the sidelines before the game during the anthem until recently. They do it now because in 2009 the Defense Department starting paying the league for patriotic displays.