Which figure of speech is used in this text?
I would remind you that extremism in the defense of liberty is no vice. And let me remind you also that moderation in the pursuit of justice is no virtue.
—Barry Goldwater, in his acceptance speech at the 1964 Republican National Convention

 - antithesis
 - chiasmus
The text uses antithesis, the contrasting of opposing ideas within a parallel grammatical structure.
Goldwater contrasts two parallel clauses, extremism in the defense of liberty is no vice and moderation in the pursuit of justice is no virtue.