I wish I’d thought of this when I was writing the column, from a reader:

Dear Jonah: I’ve always wondered if Barry Goldwater might have gotten his “Extremism in defense of liberty is no vice” concept from Martin Luther King, Jr.’s “Letter from Birmingham Jail, written the year before, which contains a long defense of the right kind of extremism: “So the question is not whether we will be extremists, but what kind of extremists we will be. Will we be extremists for hate or for love? Will we be extremists for the preservation of injustice or for the extension of justice?”

Update: Hey folks, I just want to clear up some confusion. I didn’t mean to say that I thought the above reader was right that Goldwater got the “extremism” quote from MLK. I know that Harry Jaffa is credited with penning it and that it’s an invocation of Cicero and that Karl Hess wrote the rest of the speech. I merely meant that I like the quote from MLK and wish I had incorporated it as a point in the column.