They Must Perforce Prey Upon Themselves

I am alluding of course to Albany's famous lines in Lear IV. ii:

If that the heavens do not their visible spirits
Send quickly down to tame these vile offences,
It will come,
Humanity must perforce prey on itself,
Like monsters of the deep.

It's a passage often used to express a felt disturbance at evil, as some kind of violation of a basic natural order or natural law. Something is wrong if human beings are preying upon other human beings. In our murders, treachery, and betrayals, we must be experiencing the effects of some kind of original catastrophe or upsetting of a cosmic order.

I don't know what someone convinced of metempsychosis would say of lions hunting wildebeasts, but I strongly suspect that, if deeply enough convinced of his outlook, he would view human beings' killing animals in much the same way as Albany views human beings killing other human beings. Something is wrong.

Plato's view in the end, in the Republic, is that justice, social unity, and peace can result only from our following some natural order--each doing what is his own 'work' by nature. That is why, I think, he turns almost instinctively to meat-eating when he wants to express the difference between a city founded on that sort of a natural order, and one whose social life is based upon some fundamental upsetting of that order. "Yes, we are constantly killing one another in wars. Yes, we are afflicted with ceaseless strife. But our way of life requires that. War and strife are an understandable consequence of a way of life based upon something that is fundamentally disordered. We kill and eat, without true necessity, ensouled --that is to say, rational-- beings. Is it any wonder, then, that human social life is beset with so many evils."

Someone other than Plato might have made the introduction of slavery the significant change in the transition between the healthy and luxurious state.

Plato looks at the luxurious state in much the same way that partisans of 'small is beatiful' look at the economies of Northern hemisphere countries.