If you are offended, allow me to explain
By kneeling instead of standing, you are demonstrating inferiority. While you are making a statement that some people are not being treated equally before the law, you are nevertheless behaving as if you're the lesser.
Throughout history, those considered inferior had to demonstrate their status of their inferiority by a number of ways. For example, before the Europeans retook Spain, Jews weren't allowed to build their synagogues as high as Muslim mosques; male Japanese commoners were made to shave the center of their heads; and of course, everyone must bow or kneel before a European monarch or noble. But there is another reason for it
In the US Constitution all men are created equally, so why are you kneeling instead of standing? That act makes you to look more like a lowly slave than being among equals.
Besides this, you are subverting the attention of the audience by that act. You lack proper respect that while you do not turn your back or walk away, and the kneeling seemed to present a more respectful show, you nevertheless by doing so is adding a "But" to it.
"I love my country... but the Police are a bunch of racists and Black Lives Matter!"
That makes those standing better than you are because they have more respect for the flag as it stands for freedom. You could always demonstrate later, but the standing before the flag, laying the hand to the heart, and singing of the anthem is to be done without interruption.
If you truly love your county, you should NEVER subvert the practice of it.
