I remember one of the scandals that most influenced my political thinking in recent years was the bizarre events at the animal laboratory at Huntingdon Life Sciences in 1997, when secret filming recorded employees deliberately punching the animals.
I don't mean that I am somehow putting cruelty to animals above cruelty to humans on the great moral scale, but it does set the issues in stark relief.
There were no religious or cultural or economic reasons why the animals should have attracted such malevolence. There was no civil war, no spending cuts which made them more vulnerable. Yet somehow it had become normal for a handful of employees to abuse them.
I came to the conclusion, thinking about it then, that it was a symptom of the situation: when you are allowed to inflict pain, as you are in animal laboratories, then somehow it tends to attract contempt - from the abuser to the abused.
That is a Liberal understanding, it seems to me. It means that, wherever there is a situation where the law appears to condone a power imbalance - and small abuses to humans or animals - then far worse abuse seems to become normal. It may attract cruel individuals, but the hard truth is that it doesn't seem to be about sadism by individuals - those involved collectively close their minds, eyes and consciences to it.
It isn't just a power imbalance - there are lots of them (parents and children, for example) - but it matters when small cruelties are condoned and where the world can't look inside: like a refugee camp in a war zone, or a animal testing lab, or the middle of an inaccessible jungle.
It seems incoherent, yet it also seems to happen all the time, and the devastating photos from Syria yesterday are just another example.
The nature of the regime there, and the desperate situation, seems to have created another gap - a small permission to abuse that allows in this very human, yet titanic kind of evil.
Whenever abuse appears to be allowed, even in small ways - even to animals - it appears to spread, because permission to abuse comes with contempt attached.
Now, it so happens that I am reading at the moment The Dream of the Celt, Mario Vargas Llosa's powerful novel about Roger Casement, which touches on this very issue.
History remembers Casement mainly for his trial and execution for treason in 1916, but has tended to forget the courageous and determined journeys he made, in the Congo and Amazon, documenting the horrors of the rubber trade, the gratuitous cruelty, the genocidal destruction of tribes - held violently to agreements they had signed without being able to read - the tortures and terrifying deaths inflicted on the families of anyone who dared to resist.
Mario Vargas Llosa clearly intends to indict the excesses of modern capitalism, and there is clearly an element of that. But I don't think greed really explains it. The real tragedy seems to me that both Casement's cases conform to the pattern: mild abuse is sanctioned, and - human beings being what they are - a contemptuous, genocidal heart of darkness is the result.
The novel describes Casement coming to a conclusion along these lines too, wondering why the Amazonian tribes resist so fitfully - understanding that a kind of spiritual horror overcomes them and undermines their will.
It may be, as the novel describes, that Casement concluded that this little chink which civilisation allows - with such terrifying results - is a natural result of imperialism in practice. That is why he became such a committed advocate of an Irish rising.
I read the book because an Irish friend of mine said it had convinced him that, instead of being a footnote to history, Casement was actually one of the most important Irishmen who ever lived. I am inclined to agree, despite any lingering controversy about the remainder of his life.
But when I hear about Syrian photos, it reminds me that there are deeper questions to answer beyond whatever is happening in Syria.
Why does this kind of horror happen? For a Liberal, it seems to me, there is this partial answer - it happens whenever small cruelties are allowed, and where power imbalances are sanctioned, and it happens inevitably.
But one final thought. This insight is fraught with dangers. When you seek out very small power imbalances, in search of small abuses, you can so easily become the tyrant yourself. Such are the paradoxes of human life and politics, as we are seeing in another example this week.
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