If you read through the debate you understand why things are going wrong in the West. Both the secular and the Christian participants held views which made open borders the "moral" position to take. They did so by following what you might call the "intellectual disease" which is to reduce life to a single intellectual principle and then try to derive moral positions from this single principle.
The Christian view was represented primarily by Giles Fraser, an Anglican cleric. Fraser is unusual in that he has very clearly rejected liberalism as a philosophy, but he has done so in the name of socialism (which goes to show that rejecting liberalism is only the first step, what comes next is equally important).
Fraser justifies open borders, and the massive transformation of Europe that necessarily follows, on the basis of certain passages of scripture:
The bit that comes to mind in the Scriptures for me is that very moving bit in Matthew 25 where Jesus goes, you know, "You saw me in prison, you didn't do anything, you, you didn't give me any food, I was a stranger and you didn't welcome me," and they go, "When was that?" and they say, "Inasmuch as you didn't do it to the least of these, my brothers and sisters, you did it to me." I mean, there's a whole implication there that if you're not welcoming the stranger, you're not welcoming Christ.
...you know, constantly in Jesus' teaching there's stuff about the stranger, there's stuff about the other, there's stuff about the Good Samaritan, and our moral responsibility is always to this person who is more other than us, rather than same as us.
The last line is the critical one. Fraser believes, from his reading of scripture, that our responsibility is always to those who are more "other" to us. If you believe this, then of course you're going to identify with the Muslim Africans seeking entry to Europe rather than with your fellow Europeans. Fraser, despite his repudiation of liberalism as a philosophy, has ended up with a very similar view of solidarity to liberals, namely that true solidarity is with those most other to us, rather than those we are most closely related to.
It should be said that you can see why Fraser might derive this idea from the New Testament. Jesus does emphasise in his teachings that benevolence is to be selfless (in the sense that we do not expect anything in return) and that it extends to strangers. Jesus says things like this:
But if you love those who love you, what credit is that to you? For even sinners love those who love them.
In context, Jesus is clearly emphasising that we are not to be benevolent to get something for ourselves - that is the intended message. But you can see how it might be taken to mean that the love we have for those we are related to, and who have reason to love us, is insignificant.
I don't think such a reading makes much sense. Jesus elsewhere says that in order to be saved we must honour our father and mother - why would that be so important if all that matters is our relationship to the stranger?
In practice, too, it is no small thing to love those who love us. To truly love our spouse over a lifetime, through all the stresses and hardships of life, and still to cherish them, to admire them and to find delight in our relationship with them is no small thing. To truly love our children, to have a continuing pride in our paternal relationship with our sons and to seek out an active companionship with them, to feel a loving protectiveness toward our daughters, and to be driven to provide the best start in life for our children, that is no small thing. And to love those we are related to as part of our ethny, to sense the life that we share with them and to seek to uphold the good within our common tradition - that is no small thing either.
It used to be the case that Western civilisation continued to respect these loves, but also took seriously the injunction to be benevolent to "the least among you." That gave rise to traditions of Christian charity, of noblesse oblige and of codes of chivalry.
The codes of chivalry are particularly interesting. They combined Christian benevolence (mercy, protection of the weak and the poor) with duties to countrymen and faithfulness to the church. This is a much more viable basis for a Christian civilisation than Giles Fraser's dissolving formulation that "our moral responsibility is always to this person who is more other than us, rather than same as us" - a formulation which would deliver Europe to an Islamic and African future rather than a Christian European one.