Nothing. The First Amendment allows you to pick your nose, scratch your ass or kneel during the National Anthem. Heck, you can burn the American flag or even let your dog shit on it.at this late date after we've passed square one, but what's so awful about kneeling during the National anthem? And please pardon what looks like naivety, but it looks kinda respectful to me. But then, I've always been ambivalent about the word God in the pledge to the flag too, since it first appeared in 1954, a year after I graduated high school..meaning I never said it all thru my youth because it was added later. Does that mean that all of us who grew up pre-God in the allegiance are unpatriotic? And FYI, I still call it the Army Air Corps.
OTOH, what is wrong with other Americans disapproving of your actions? Don't they have rights too? What's wrong with the owner of a business terminating an employee because that employee's public political demonstrations are casting a bad light on the business?