I said that no party held the privilege of dictating to me how I should vote. That if party loyalty was a form of patriotism, I was no patriot, and that I didn’t think I was much of a patriot anyway, for oftener than otherwise what the general body of Americans regarded as the patriotic course was not in accordance with my views; that if there was any valuable difference between being an American and a monarchist it lay in the theory that the American could decide for himself what is patriotic and what isn’t; whereas the king could dictate the monarchist’s patriotism for him–-a decision which was final and must be accepted by the victim; that in my belief I was the only person in the sixty millions–-with Congress and the Administration back of the sixty million–-who was privileged to construct my patriotism for me.
They said “Suppose the country is entering upon a war–-where do you stand then? Do you arrogate yourself the privilege of going your own way in the matter, in the face of the nation?"
“Yes,” I said, “that is my position. If I thought it an unrighteous war I would say so. If I were invited to shoulder a musket in that cause and march under that flag, I would decline. I would not voluntarily march under this country’s flag, nor any other, when it was my private judgment that the country was in the wrong. If the country obliged me to shoulder the musket I could not help myself, but I would never volunteer. To volunteer would be the act of a traitor to myself, and consequently traitor to my country. If I refused to volunteer, I should be called a traitor, I am well aware of that–-but that would not make me at traitor. The unanimous vote of the sixty millions could not make me at traitor. I should still be a patriot, and, in my opinion, the only one in the whole country.
Stirring words. [As seen in Harper's Magazine, April 11, 2011, pp. 35, "Democracy 101," quoting from The Autobiography of Mark Twain, Vol. 1.]
Bonus: below is Mark Twain's response to a letter regarding a library's removal of Tom Sawyer and Huckleberry Finn from the children's section:
"I am greatly troubled by what you say. I wrote Tom Sawyer and Huck Finn for adults exclusively, and it always distresses me when I find that boys and girls have been allowed access to them. The mind that becomes soiled in youth can never again be washed clean; I know this by my own experience, and to this day I cherish an unappeasable bitterness against the unfaithful guardians of my young life, who not only permitted but compelled me to read an unexpurgated Bible through before I was 15 years old. None can do that and ever draw a clean sweet breath again this side of the grave."
More here. (November 21, 1905, letter to Asa Don Dickinson)
Bonus II (added September 2016): "If there is any fixed star in our constitutional constellation, it is that no official, high or petty, can prescribe what shall be orthodox in politics, nationalism, religion, or other matters of opinion or force citizens to confess by word or act their faith therein." -- Justice Robert H. Jackson, West Virginia State Board of Education v. Barnette, 319 U.S. 624, 642 (1943).