The anthem protest is the most effective tactic Colin Kaepernick could use.
To be effective, a protest needs to get attention.
At times, it must be discomfiting to the comfortable.
Especially if you are protesting as an individual.
If he had used any of the "acceptable" methods(writing to a politician, joining a march, even giving a speech, no one would have noticed and no one would have cared). At the same time, he avoided more drastic methods of expression...burning a flag, physical violence against others...that would only have caused backlash.
He made the statement, made his position clear, took the criticism and even abuse with dignity and courage, and showed more courage in doing so than any American athlete since Muhammad Ali, John Carlos and Tommie Smith when they walked the walk for what they believed in.
Colin Kaepernick may have brought his career to an early end. He will likely be a pariah in the bigoted, reactionary, economic-royalist world of the NFL. He has almost certainly cost himself tens of millions of dollars. And in doing so, he has made sure this nation kept paying attention to an issue it was already beginning to forget-the daily violent repression faced by people of color in this country, no matter what they do or how well they do it.
Any other choice, any other tactic he could have used would have been futile and irrelevant.