The short course on freedom of speech (expression): Person A has the right to say anything he pleases, or kneel for the national anthem, so long as doing so does not place anyone in IMMINENT danger. Person B has the right to oppose Person A's views, and to denounce them 'til his heart's content. Neither has the right to interfere with, or prevent, the other's expression(s).  And yes, the First Amendment covers even the most vile hate speech imaginable. That was the entire point of the Courts' rulings vis-a-vis the Nazi's Skokie march.