Constitutional rights trump all other considerations.   Kaepernick can be fired for his protest, but constitutionally, the NFL cannot make Kaepernick's job dependent on him NOT exercising his civil rights.    That would be a violation of his constitutional rights.    

What you don't understand is that you are NOT doing the same thing he is.    You are doing something else altogether, and the only commonality between your stated views and Kaepernick's act of protest is that no one is arresting you.   Other than that, your criticism has little to nothing in common with Mr. Kaepernick's act of protest.