Good quotes about slavery and the abolition of slavery

“I have observed this in my experience of slavery, - that whenever my condition was improved, instead of its increasing my contentment, it only increased my desire to be free, and set me to thinking of plans to gain my freedom. I have found that, to make a contented slave, it is necessary to make a thoughtless one. It is necessary to darken his moral and mental vision, and, as far as possible, to annihilate the power of reason. He must be able to detect no inconsistencies in slavery; he must be made to feel that slavery is right; and he can be brought to that only when he ceased to be a man.”
― Frederick Douglass (abolitionist), Narrative of the Life of Frederick Douglass

General quote, which can be applied both for human rights and rights of non-human animals.
"As I told my students at the start of my courses, "You can't be neutral on a moving train." That is, the world is already moving in certain directions—many of them horrifying. Children are going hungry, people are dying in wars. To be neutral in such a situation is to collaborate with what is going on. The word "collaborator" had a deadly meaning in the Nazi era. It should have that meaning still.

"Therefore, I doubt you will find in the following pages any hint of "neutrality." -- Howard Zinn (author, historian and social activist)