Which is, of course, beyond laughable and beyond contempt.
This is a fair point. I have often thought that the Eurabia scenarios were not well thought-out demographically. This is not to say that they're false, just that they aren't really proven. A few weeks back I posted this, which was relegated to the bloggers' forum and didn't draw much comment. It was the only systematic attempt I could find to actually run numbers on the Muslim population in Europe. (Which doesn't even take account of the extent to which Muslims can be and are assimilated).
If it's true, the Eurabia scenario is a disconcerting one, but whether it's true is still very much up for debate IMHO. Population projections are very unreliable, and so we're all working with very little here.
OTOH, the people you quote are probably too optimistic:
Let's also assume that the white folks of the EU have zero population growth.
In fact, it seems to be true that European populations, other than immigration, will begin shrinking in the next few years. But the whole issue is so inflammatory that AFAIK no good demographer has ever tried to break down European demographic projections by race or religion.
IMHO one of the difficulties the Euro-optimists in attempting (or truly) rebutting Steyn is he moves in the same insider circles as them when it comes to Euro and British politics. He personally knows Giscard d'Estang, Chris Patten explicitly names him in derision, he knows the British establishment. So far I think only some continental Euros had seriously attempted to rebut him - American leftists no longer have the capacity of arguments.
Anyway, this is just my guess, and given that Steyn reads FR perhaps he will respond to the challenges you found on the net in some of his tidbits or future articles?
If a million Dutchmen head for North America, that would certainly influence the demographics.