A flag is just a piece of cloth. What it's supposed to represent - an equal playing field for all, justice for all - is not being adhered to and has not been, ever, in the history of the US.
Remember these protests started under Obama's administration, as a protest against police brutality. Only Trump could make it all about himself and some perverse idea of patriotism, where one doesn't question how loyalty to this 'flag' trumps (pun intended) keeping racist law enforcement officers in check.
But since The Donald has decided to put his rather profane tuppence ha'porth in, let's use it to question what is really important here. In truth, no flag matters. What is done supposedly in the name of the flag does. The flag is no more than a human extension of the Pavlov's dog experiment. I support those taking a knee because what they are protesting for (actual civil rights, the right to not be killed by endemic racism) is more important. If you are proud of your country (and by this I mean any country, not just the U.S.), know exactly what it is you're proud of. When it comes down to it, and if one's grasp on history is solid, and if one is scrupulously honest, it'll end up that you'll be proud of some things, of other things not so much. Let the country that is without sin cast the first stone.
The danger is, during this political paradigm shift (and we are still in the midst of this shift) that revisionism of history is rife. We have the situation in Germany where partly (to the best of my understanding) what the AfD set their stall out on is whitewashing German history, especially that of the Third Reich, as something to be proud of, that 'others' had wilfully misinterpreted. How can one be proud of that part of one's history which included mass genocide? And this point could be said of many countries, including the US. Including the UK. Trump and Brexit happened, to a large extent, due to people's ignorance of their own imperialist, genocidal, racist histories.
Pride in a flag, for pride's sake, if the foundation of what that flag represents, is ridiculous. Pride in an anthem, a song, is indefensible if the human rights that have been nominally enshrined in law are not being accorded to all citizens, irrespective of colour, creed, sex, gender, sexual preference, power and wealth status. There is ample evidence to show us that the US has little respect for the rights of its African-American citizens. The very presence of a man like Trump in the White House and his penchant for the company of white supremacists and self-described Nazis is a very testimony to this. The symbols that we once held dear unquestioningly are being called into question. It's long overdue. Men like Kaepernick remind us that rather than slavishly adhering to the status quo, our citizenship calls upon us to question whether it is fit for purpose, or indeed, if it ever was. And the evidence and history taken objectively, would strongly indicate that it never has been.
The late great Stéphane Hessel wrote about a 'Time for Outrage'. Outrage is only the beginning point. It's the precursor of change, and holds the potential of change for the better, for everyone. Some people will not want change, simply because change, even when it is for the better, is not easy. Some people will not want change, because they see change as an attack on their status and supremacy in the world order. Those latter are probably not wrong, but they must not stand as an impediment to change for the better for the majority. We are on a knife's edge balance in the West when Germany, for 28 years a beacon of hope to the power of people and progressive thinking, to the art of the possible rather than the cynical deal, can have 1.3 citizens who ignored their own history and voted in the far-right to the Bundestag again. The damage has been done, and nationalism has made its inroads. The road that this ultimately leads to can be changed, however. It's not too late for that yet, if we remain conscious of the difference between superficial nationalism and deeper citizenship.
Nationalism only appeals to those who are childish and sheep-like in their thinking. Those who deal in the vicious pettiness of playground politics. Those who like their inane saluting, doublespeak, symbolism and who find comfort in the denigration of others. This is not 'love of country'. Love of country, and deeper citizenship is when you care that everyone is afforded the same rights, the same opportunities, that everyone prospers. That's what those who are taking a knee are highlighting. May they overcome.