The animal liberation movement is saying that where animals and humans have similar interests - we might take the interest in avoiding physical pain as an example, for it is an interest that humans clearly share with other animals - those interests are to be counted equally, with no automatic discount just because one of the beings is not human.
Peter SingerWhereas the property-owning middle class could win freedom for themselves on the basis of rights to property--thus excluding others from the freedom they gain--the property-less working class possess nothing but their title as human beings. Thus they can liberate themselves only by liberating all humanity.
Peter SingerSuppose I grant that pigs and dogs are self-aware to some degree, and do have thoughts about things in the future. That would provide some reason for thinking it intrinsically wrong to kill them - not absolutely wrong, but perhaps quite a serious wrong. Still, there are other animals - chickens maybe, or fish - who can feel pain but don't have any self-awareness or capacity for thinking about the future. For those animals, you haven't given me any reason why painless killing would be wrong, if other animals take their place and lead an equally good life.
Peter SingerI believe that in this new world that we live in, we often have a responsibility, you know, to actually go beyond the thou shalt nots - that is, the not harming others - and say we can help others and we should be helping others.
Peter SingerAll the arguments to prove man's superiority cannot shatter this hard fact: in suffering, the animals are our equals.
Peter SingerMy aim is to advocate that we make this mental switch in respect of our attitudes and practices towards a very large group of beings: members of species other than our own - or, as we popularly though misleadingly call them, animals. In other words, I am urging that we extend to other species the basic principle of equality that most of us recognize should be extended to all members of our own species.
Peter Singer