“Blasphemy is an epithet bestowed by superstition upon common sense.”

"To the Indianapolis Clergy." The Iconoclast (Indianapolis, IN) (1883)
Source: The Works of Robert G. Ingersoll, Vol. V
Context: I do not rely upon superstition, but upon knowledge; not upon miracles, but upon facts; not upon the dead, but upon the living; and when we become absolutely civilized, we shall look back upon the superstitions of the world, not simply with contempt, but with pity.
Context: What is blasphemy? I will give you a definition; I will give you my thought upon this subject. What is real blasphemy?
To live on the unpaid labor of other men — that is blasphemy.
To enslave your fellow-man, to put chains upon his body — that is blasphemy.
To enslave the minds of men, to put manacles upon the brain, padlocks upon the lips — that is blasphemy.
To deny what you believe to be true, to admit to be true what you believe to be a lie — that is blasphemy.
To strike the weak and unprotected, in order that you may gain the applause of the ignorant and superstitious mob — that is blasphemy.
To persecute the intelligent few, at the command of the ignorant many — that is blasphemy.
To forge chains, to build dungeons, for your honest fellow-men — that is blasphemy.
To pollute the souls of children with the dogma of eternal pain — that is blasphemy.
To violate your conscience — that is blasphemy.
The jury that gives an unjust verdict, and the judge who pronounces an unjust sentence, are blasphemers.
The man who bows to public opinion against his better judgment and against his honest conviction, is a blasphemer.
Why should we fear our fellow-men? Why should not each human being have the right, so far as thought and its expression are concerned, of all the world? What harm can come from an honest interchange of thought?