Unlike the Stolen Generations and the abuse of children by priests, when historians look back on our treatment of asylum seekers they won't be able to say, "most people didn't know what was going on", writes Hugh Mackay.

In the future, when historians try to comprehend Australia's shocking asylum seeker detention policy, there's one thing they won't be able to say in our defence. Unlike the case of the Stolen Generations of Aboriginal children, or the sexual abuse of children by priests, they won't be able to say, "most people didn't know what was going on".

They won't be able to say it because it simply isn't true. Is there a single Australian who doesn't know about the impact on mental health of life in our detention centres? Does anyone not realise we have been deliberately demonising and dehumanising asylum seekers who have fled their homeland, at great personal risk, in those notorious boats? Could anyone be ignorant of the findings of the Human Rights Commission's report into the damage we are doing to children in detention?

We rise up - as we should - when Indonesia threatens to execute Australian drug traffickers. But where is our rage, our shame, in the face of a policy that, for many asylum seekers, will amount to a kind of slow death? Their eroding mental health is associated not just with the loss of freedom, not just with the privations of a quasi-prison, but also with the rising sense of despair as it dawns on them that our Government means it when it says "these people" will never settle in Australia.

Perhaps some of us don't grasp what's happening in the rest of the world. Perhaps we don't realise that the trickle of hapless asylum seekers coming to Australia is a mere drop in the ocean of misery that is the global refugee problem. Tens of millions of people, tonight, have nowhere to call home - at least, nowhere to call a home that is safe and secure. How can we escape our moral responsibility to respond to the cry for help from the few who have made it to our shores?

Those future historians trying to comprehend how an otherwise civilised society could so brazenly breach its human rights obligations, might phone their mates in the moral philosophy department for help. "What was their justification?" they will ask. "How did they convince the voters to support them?"

"Ah," the philosophers will reply, "they simply appealed to the murkiest and most slippery moral principle of all, and made it seem plausible."

"There was a moral principle at work here?"

"A dubious principle, but still, a principle: the end justifies the means. The very same principle used to justify torture, political assassination, bribery and corruption of all kinds. How else can you explain successive governments' argument that this was how you stop the boats? And, just like the torturers, they were able to show that it works - see for yourself!"

In an attempt to quell any moral squeamishness, governments have employed two supporting arguments. First, "we are trying to stop people drowning at sea". This is nonsense, of course: if that were the real issue, we'd have a fleet of planes and boats spotting and rescuing people from unseaworthy boats.

The second argument is a corker: "We want to discourage people smugglers." It goes without saying that we want to discourage people smugglers, but there are two quite distinct moral questions here: how do you stop people smugglers from exploiting the vulnerable? And - separate question - how do you treat people once they have arrived on our shores?

To conflate the two is either reckless or dishonest. The problem of people smuggling must be addressed by skilful diplomacy, regional co-operation, and relentless policing, not by punishing those who have already arrived in search of asylum.

There's a sting in the tail of this story. For any government with a black hole like this one at its moral heart, other moral lapses become correspondingly easier. For example, once you have implemented a policy that hits desperate refugees where it hurts most, denying them identity, dignity, freedom and hope, it becomes easier to be tough on your own poor, elderly, unemployed and marginalised. (Recognise any recent budgets in there?)

Governments that fail to provide moral leadership will inevitably lose their moral authority. And that's a loss that diminishes us all.

Hugh Mackay is a social researcher and the author, most recently, of The Art of Belonging (published by Macmillan). He is a patron of the Asylum Seekers Centre.