Perhaps for the sake of being clever, John Derbyshire ignores a thing that is very odd for a conservative writer to ignore. Granted, the related twofold goals of his review of Robert Spencer’s book Religion of Peace? — Why Christianity Is and Islam Isn’t give him a narrow context in which to work. It would be difficult, I’ll concede, to argue both that Christianity and Islam are alike in their “magical thinking,” which must necessarily make way for the advance of secularism among those with empirical inclinations, and that the “moral universalism” and “humane forbearance of the Prince of Peace” are the West’s weaknesses (not secularism) against the Islamofascist threat, while still admitting that a great many of the strongest advocates against that ideology’s encroachment count themselves as followers of said Prince.
Derbyshire manages to leave this consideration out of his piece through the tidy mechanism of a declaration that “Spencer can’t have it both ways.” That is, he can’t insist that Christianity contributed much that Derbyshire agrees is good in Western society — “science and political progress” — without also having contributed to the unthinking (and suicidal) acceptance-ism that tends toward “impulses to hate [their own] culture and yield to its enemies.” Through this mechanism, it becomes Derbyshire who gets to have it both ways. Toward his first goal:

To us pagans, it looks rather as though science only really got going when the power of faith had ebbed from its late-medieval high point; and then, it got going mainly in those north European nations that had embraced Protestantism after the Reformation. …
To people who eschew such [magical] thinking — people who prefer to ground their beliefs in the strict rules of evidence used in modern law and science — Mohammed’s flying through the air to Jerusalem on a white steed is no more preposterous than the doctrine of the Immaculate Conception; and so, God’s instructions to us through Mohammed are no more or less likely to make us better or worse than his instructions through Christ.

But toward his second:

It may even be that Robert Spencer suspects, at some level, that this sickness in the Western soul has its roots in Christianity, just like — according to him — every other aspect of our civilization.

Derbyshire may cloak his reference to the Christian “sickness” with a “may” and an “according to,” but a fair reading of what follows suggests that it is, in fact, what he himself believes to be true. So, from his point of view, no, Christianity did not provide “the seed-bed from which modern science grew,” but yes, it did conspire — two millennia into its lifespan — to make us cowards perhaps fated to a “religion of slaves.”
A bit of common knowledge that Derbyshire gives not the merest consideration is that the “diversity” and open-borders movements are of secular and progressive origin, with their roots at least in part in relativism about such things as religion — the very relativism that he displays when he compares “preposterous” doctrines. The West’s potentially fatal problem isn’t that Christians believe that they must roll over for conflicting ideologies in the name of peace, but that secularism, both of itself and in the degree to which it has corrupted Christianity, has promoted the idea that it doesn’t matter whether or not Christianity is true.
This is why — or one reason why — he errs in his suggestion that “even if it were true that the church midwifed science… following delivery of the newborn, the midwife’s services are no longer required.” The metaphor (although no doubt carefully chosen for this reason) wrongly excludes the possibility that the church has a crucial role to play in a scientifically educated society. Christianity produces “a civilizationally-suicidal view” only when blended with the notion that the religion itself doesn’t matter, whether the destruction comes at the hands of a more aggressive converting power or as a result of unfettered “advancement” plucked clean of inconvenient moral restrictions.
Derbyshire picks the anti-religion provocateur Christopher Hitchens as his example of a secularist whom he’d trust for “standing and fighting against jihadism” more than a Christian and the dhimmitic, retiring Dutch Roman Catholic Bishop Tiny Muskens as his example of why. Once again, the key is that which is ignored: these two men are notable mainly for their uniqueness within their categories. When the jihadis come a’callin’, whom would you rather have on your side: Derb’s conservative Christian peers or the world’s secular liberals? Obviously the former, because people with faith in their own beliefs will defend those beliefs, even if they scrutinize a doctrine of just war as they do so.