[Henry] Spira has a knack for putting things plainly. When I asked him why he has spent more than half a century working for the causes I have mentioned, he said simply that he is on the side of the weak, not the powerful; of the oppressed, not the oppressor; of the ridden, not the rider. And he talks of the vast quantity of pain and suffering that exists in our universe, and of his desire to do something to reduce it. That, I think, is what the left is all about. There are many ways of being on the left, and Spira’s is only one of them, but what motivates him is essential to any genuine left. If we shrug our shoulders at the avoidable suffering of the weak and the poor, of those who are getting exploited and ripped off, or who simply do not have enough to sustain life at a decent level, we are not of the left. If we say that that is just the way the world is, and always will be, and there is nothing we can do about it, we are not part of the left. The left wants to do something about this situation.

Peter Singer, A Darwinian Left, New Haven, 1999, pp. 8-9