The first principle of a free society is an untrammeled flow of words in an open forum.

Adlai Stevenson (1900-1965) American diplomat, statesman

Speech (1961-01-18), US Senate Committee on Foreign Relations, Washington, DC
    (Source)

Statement given by Stevenson after his nomination by President-elect Kennedy to be ambassador to the United Nation, which office he held until his death in 1965. The speech (or this passage) is often cited to the New York Times coverage of it the following day, though often mistakenly dating it in 1962.

In context, he is addressing criticisms of the UN as a "debating society," noting that the US Congress often serves as such, from which he extends this principle.