Kaepernick has individual earnings that put him into a rare bracket that few will ever experience. Kaepernick is a name known by, likely, tens of millions of the consumer public which in itself carries a rarely experienced level of power (speech). Due to this he himself could fund a range of activities for movements that espouse his point of view. Further, he can attract the attention of public informational outlets that will amplify his opinions to a wide audience.
Bottom line, he has an elite level of ability to aid a cause. However, choosing a venue full of people who the vast majority will never see that rare bracket of earnings, likely paid a significant amount to see a 'game', and a significant portion will not ever agree with his opinion? I have my doubts that this assists his cause unless his cause was to get his name repeated in the media.
Though virtually all players do from a patriotic, political, corporate, or socially acceptable reason, the NFL does not require Kaepernick to stand during the national anthem. IMHO from a gameday perspective that's that.
Kaepernick also chose to let the public, conspicuously it seems, know the reasons he did not stand (he dislikes the United States for his stated reasons). This makes him, most especially due to his celebrity status, absolute fair game for the public's opinion, ridicule, scorn, support, ambivalence etc. And there is/was no danger to free speech occurring with any of it (there is danger to free speech but it's not because of Kaepernick's action or those commenting on his action).
