Ah, the old "historical inevitability" thing - one reason this is not an issue of the Left is that there are an awful lot of disappointed true believers over there who are still desperately holding out for their own form of historical inevitability, wherein capitalism founders from its own internal contradictions and a new socialist utopia eventuates. To the Islamists it's the same metaphor - only the utopia takes a different form. Both are fated to be disappointed in the end, I suspect, but that doesn't mean the road from here to there isn't going to be as bloody as the road from 1917 to 1989 turned out to be.
I am less alarmed than Steyn with respect to the ability of Western society to function on a less-populated and older-median-age model. Given a measure that doesn't figure into these calculations, i.e. the longer span of productivity of latterday humanity and the help that technology promises with respect to yet longer health, it appears to me that we might very well ride out this period of low birthrate, in the absence of demographic changes produced by migration. That's always the issue - history is, if it may be distilled to one single measure, the story of migratory peoples coming on new land, very little of which was unpopulated before they happened along. In that sense I think Steyn correct when he blows the warning horn on the influx of the unassimilatable. It is this, and not just birthrates, that is the immediate peril for Europe, IMHO.
Another interesting side effect of Muslim extremism is that it dends to de-assimilate moderate Muslims and absorb them. Moderate Muslims in Europe tend to fall under the orbit of extremists once they start gaining enough gravity. This is reflected in an increase in radicalization of second and even third generation immigrants.
Granted, European countries often exacerbate this problem by failing to thoroughly assimilate their immigrants in the first place. The isolated North African ghettos of Paris are the perfect incubators for radical Wahabbism, even if they are mostly moderate now. Muslim Europeans that are treated like strangers in their own country will be easy prey for would be Abu Musab al Zarqawis with dreams of insurgency and revolution.
You've nailed it (with your drill?). The admission of large numbers of immigrants with a very different culture is very dangerous -- just ask the American Indian.
You nailed it. The demographic portion Steyn's argument is a variant of The Vision Of The Anointed -- alarmed that people left to their own devices don't do what he thinks they ought to do (e.g. have more kids), he builds a doomsday case by ignoring the positive results of cumulative individual decisions (e.g. concentrating more attention on fewer warm bodies cranks up per-capita productivity).
"Ah, the old 'historical inevitability' thing - one reason this is not an issue of the Left is that there are an awful lot of disappointed true believers over there who are still desperately holding out for their own form of historical inevitability, wherein capitalism founders from its own internal contradictions and a new socialist utopia eventuates."
Which is probably why the multiculturalism model arose.
If you devise a system where unassimilatable peoples are given a substancial amount of autonomy in their own communities, in your homeland, you still maintain the overarching power of the state. More foreigners, yes, but the same white ruling class. At least for the time being.