You could have asked the same question to the Roman Empire. It's decadence. Confronted with a threat, decadent cultures tend to navel-gaze, and to assume that the other side is just like them. The misapprehension that the other side wants to be left alone leades to a tendency to ignore, rather than to deal with the threat.
Steyn, BTW, nails the threat: it's not Islam per se, but rather the ideology and practitioners of Wahabism. Deal with those nice people, and the rest (and majority) of Islam will eventually emerge from the 7th Century.
I was reading Frederick Hayek's "The Road to Serfdom" the other day and in it he posits that after WWI we became what we defeated in otherwords Nichean nihilists. IOW The west is a suicidal culture intent on ending itself. Jihad is just the latest, newest tool.
Actually, it is the Communists who are reenacting the Phoenix scenario and they are the ones trying to bring down Western civilization. Multiculturalism is simply one of their tactics.
Who keeps the racial pots boiling? Who promotes, no insists upon, political correctness and multiculturalism? Who divides women from men? Who keeps the poor in poverty with programs supposedly designed to get them out of it but is really just an extension of big government?
The answer in this country is the Democrats. The Democrats are following the principles of Communism and have strong ties to Communism, though they will scream if you confront them. The Democrats are our enemies just like their allies the terrorists. We should treat them as such.
Well, since you have set the rules... :)
Why are the Western nations acting like they want this conflict to bring them down?
Is it just multiculturalism gone haywire? Or is is a "Phoenix" scenario they're looking for?
Perhaps it's because the leaders of those Western nations are more interested in and so focused on completing their own agendas for consolidation of their own mastery over their own subjects, err... citizens, that they're either blind to or fatally underestimating the threat?
There are some with what I call a "Nero" complex. They're willing to destroy in order to rebuild according to their own design.