“To us it seems incredible that the Greek philosophers should have scanned so deep into right and wrong and yet never noticed the immorality of slavery. Perhaps three thousand years from now it will seem equally incredible that we do not notice the immorality of our oppression of animals.”

1960s, Letter from a Birmingham Jail (1963)
Variant: I must affirm that it is just as wrong, or perhaps even more so, to use moral means to preserve immoral ends.
Context: I have consistently preached that nonviolence demands that the means we use must be as pure as the ends we seek. I have tried to make clear that it is wrong to use immoral means to attain moral ends. But now I must affirm that it is just as wrong, or perhaps even more so, to use moral means to preserve immoral ends.

As quoted in " Desmond Tutu turns 75 http://www.news24.com/World/News/Desmond-Tutu-turns-75-20061006" at News24 (6 October 2006)

Source: Leaving Home‎ (1987), p. 20

Source: The Light of Day (1900), Ch. IV: Natural Versus Supernatural

Rex Stout, page 246
Invitation to Learning

Source: Cry Wolf

Source: The Slavery of Our Times (1890), Chapter 8: Slavery Exists Among Us

The human conscience knows no distinction between church rates and other compulsory rates and taxes. The sin lies in the disregarding of each other's convictions, and is not affected by the subject matter of the tax.
The Principles of Voluntaryism and Free Life