Weirdly enough, possibly my favourite quote that I have discovered so far is by a US American, the socialist Eugene Debs.
"Years ago, I recognized my kinship with all living things, and I made up my mind that I was not one bit better than the meanest on earth...While there is a lower class, I am in it, while there is a criminal element, I am of it, and while there is a soul in prison, I am not free."
Eugene V. Debs
1855-1926.