So now we have deserving and undeserving migrants. Police in Sicily arrested 15 Muslim boat people rescued from a leaky rubber dinghy after other survivors accused them of having thrown 12 Christian passengers overboard in a dispute about religion. Perhaps this new moral category may help ease European consciences over the 22,000 desperate people who have died crossing the Mediterranean from Africa since the year 2000. We now have innocent migrants to contrast with guilty ones, good migrants and bad, or perhaps we should say bad migrants and worse migrants.

We can add that to our existing hierarchy of moral culpability. Refugees are somehow accorded an ethical superiority over economic migrants because they are escaping persecution, rather than merely wanting a better life. Yet, in Africa, the migrant is celebrated as a contemporary hero, the daring risk-taker.

Two kinds of response govern our attitude to the arrival of the stranger. One is conditioned by a sense of affluence. It is rooted in empathy. It is the impulse to help. The other is fostered by an anxiety of scarcity. It is embedded in fear. It is the impulse to slam shut the door.

Modern politics is dominated by, and often reduced to, economics. The idea of competition for scarce resources is nowadays our default. We are being swamped. They are taking our jobs, or at least our benefits. This response is at its most brazen in the rhetoric of Ukip, but it is the underlying paradigm of most mainstream politicians who believe it is what voters think.

The paradox is that we British also pride ourselves on our communal compassion. It was shocking to hear yesterday that one million food parcels were handed out last year in the UK, the world’s sixth-richest economy. But that statistic also means that ordinary Britons have donated a million parcels to food banks for those in need. As a nation, our response to natural disasters across the globe is routinely generous. Donations to big charity events rise year on year; Comic Relief has now raised more than £1bn since it started 30 years ago.

As a nation, we flip back and forth between fear and compassion. Or perhaps we even hold them in a constant tension in our politics. It is why, despite the cries of conservative backwoodsmen, all our mainstream parties go into the present election committed to the UN target of giving 7p of every £10 the nation earns to international aid and development. And yet, at the same time, Britain has shamefully refused to contribute to the paltry budget of Frontex, the EU border agency whose tiny force of six ships, two aeroplanes and one helicopter patrols the Mediterranean to spot leaky boats filled with desperate Africans making for Europe’s shores.

The coalition argues against putting in any money to that search-and-rescue operation, claiming that it creates a “pull factor”, drawing Africans across the water. This is as specious as it is shocking. Migrants interviewed by human rights groups are almost all unaware that such a rescue operation exists. And though the Frontex operation runs at just a third of the capacity of the Italian government’s Operation Mare Nostrum, which Frontex replaced, the numbers have not dropped – as the “pull factor” argument would suggest. Instead, last year they soared – with a record 170,000 making the perilous crossing to Italy, almost 9,000 of them in the past week alone.

What drives them are the “push factors” of poverty, disease, war and collapsing states in Libya, Iraq, Syria and sub-Saharan Africa and the advance of the jihadist terrorists of Islamic State (Isis) and Boko Haram. There is a grim irony in the fact that, in Iraq and Libya, the West removed the controlling tyrants Saddam and Gaddafi, and, in Syria, it has half-heartedly tried to do the same. Two British prime ministers, Tony Blair and David Cameron, were key players in that.

“We will stand with you every step of the way,” Cameron said, as he stood in Martyrs’ Square in Tripoli and declared that Libyans had “no greater friend than the United Kingdom”. Hollow laughter in Libya. The price of Blair’s war in Iraq was painfully catalogued in a BBC film, Kill the Christians, by the courageous Jane Corbin on Wednesday; Iraqi Christians are today punished by Isis for the sins of the Western “crusaders”. All of which suggests that we actually have a greater moral responsibility to help, instead of washing our hands of the resulting chaotic vacuums into which the worst kind of fundamentalism has rushed. They are not stealing our jobs; we have stolen theirs, and their homes, and even their lives. The bodies that are washed up on Europe’s shores are the flotsam of our failed foreign policies.

An election offers an opportunity to remind ourselves of an alternative narrative. For all the talk of austerity, we live in an economy of abundance – in global terms, at any rate. We need to remind ourselves that immigration enriches rather than impoverishes, both economically and culturally. Even Italy needs more migrant labour than it currently uses, to support its ageing population – though it also needs the rest of Europe to share the burden it is bearing disproportionately at present.

“We have a duty to save lives,” said Italy’s Foreign Minister, Paolo Gentiloni, appealing for international help because 90 per cent of the rescue effort is falling on the Italian navy. The British navy, which readily played its part in the bombing of Libya from which the migrants now flee in their overcrowded and ramshackle craft, is doing nothing. The next British government must rectify that.