To return to brass tacks – we each inhabit a planet of 7.8 billion singular, unique and isolated consciousnesses, each afflicted by terrible loneliness. We yearn, above all else, for communion and community (presumably because intuitive co-operation gave early humans distinct advantages), yet we are incapable of direct access to a single other mind.
On the other hand, we are designed to generalise and be suspicious of newness and difference. This, again, was probably a survival trait in earlier times (“who’s this huge hairy creature with all the teeth? He’s new around here. I must introduce myself…”)
This tension remains unresolved in the human psyche and leads to tribalism, prejudice and discrimination. We huddle into our own little groups, from which we derive social identity and a sense of belonging, often defining our tribe by its difference, even opposition, to others, who we characterise according to our needs. Ostracism from our group would bring great suffering, so we are all anxious to toe the line and keep to the rules.
How can we escape the prejudice and antipathy, the persecutions, even genocides, that result from these fundamental aspects of the human brain? How can we guarantee that our tribe won’t fall apart from factionalism, or fall prey to more powerful tribes, or that we won’t be banished from our tribes for being too different?
We must all agree that a self of the same substance, an equal flame of sentience and feeling, resides in each of us. And we must recognise and salute that common humanity with equal respect. In other words, we must all, explicitly, consciously, agree to treat everyone, each individual, equally. Only by promising to do well by others can we trust them to do well by us. You can’t stop a street fight by shouting “Ok! Everybody put down your weapons! Unless, of course you feel you have a genuine grievance. In which case, please, keep stabbing.” Everybody needs to stop hurting everybody else. Right now. No matter how badly they’ve been hurt in the past.
The law must be impartial. It must apply equally to all.
 And who’s to say animals aren’t similarly troubled, as I’ve said before? Perhaps conflicting impulses are at war within their breasts and, while they act upon the dominant, they are still wordlessly anguished. Perhaps the fox is horrified by what he’s been driven to do to your chickens. Adult pet rabbits suffer from loneliness, apparently, yet if introduced to other adults, they will fight. To live is to feel anguish.