The last lesson a man ever learns is, that liberty of thought and speech is the right for all mankind; that the man who denies every article of our creed is to be allowed to preach just as often and just as loud as we ourselves. We have learned this, — been taught it by persecution on the question of slavery. No matter whose lips that would speak, they must be free and ungagged. Let us always remember that he does not really believe his own opinions, who dares not give free scope to his opponent. Persecution is really want of faith in our creed.

Wendell Phillips (1811-1884) American abolitionist, orator

“The Boston Mob,” speech, Antislavery Meeting, Boston (21 Oct 1855)
    (Source)

"On the Twentieth Anniversary of the Mob of October 21, 1835."