There is such a thing as legitimate protest, something Martin Luther King showed us, and when it is to protest real injustices in the present moment, then perfectly legitimate.
However, that is not what BLM and those refusing to stand and be part of the National Anthem or the Pledge are doing. The coach to took his team out on the field and pointed out that they had not earned anything they currently enjoyed, neither did he, but it was the sacrifices of those in the military, of those who work to keep our streets safe etc… who earned them what they have by protecting the freedoms that they seem not to understand or value, though they think they are fighting against oppression etc.. If they lived through what my mom lived through during fascism, or if they had to live under strict Sharia, they might not be so disrespectful to the Anthem, the Flag, all of that which are the foundations along with our Constitution. As for law enforcement personnel and military personnel, granted not everyone is perfect, mistakes are made. However, if you are going to be lawless, act in a lawless and rebellious manner when in the presence of law enforcement and such, do not expect a smile and chocolates. There are consequences to actions, to life choices. If BLM, these sports figures really wanted to be constructive then they would use their money, their influence for getting rid of gangs, pushing community leaders to stop causing division, to stop the race baiting, create school choice, look at how policies of the left have destroyed them as has race baiting, and a victim mentality.
Even in our education system, this notion of not offending, of PC and yet at the same time brainwashing to hate America, hate the flag, white privilege, all of that is nonsensical nonsense that does a great deal of harm to the fabric of our Democratic Republic. This is leading us on a very dangerous path, this lack of respect, this PC, all of it, a very dangerous path.