Tom Sowell takes on all that and more in one, brief, incisive op-ed. A few excerpts:

Iraq is only the latest in a long series of catastrophes growing out of diversity. These include “ethnic cleansing” in the Balkans, genocide in Rwanda and the Sudan, the million lives destroyed in intercommunal violence when India became independent in 1947 and the even larger number of Armenians slaughtered by Turks during World War I. Despite much gushing about how we should “celebrate diversity,” America’s great achievement has not been in having diversity but in taming its dangers that have run amok in many other countries. Americans have by no means escaped diversity’s oppressions and violence, but we have reined them in.

He also argues:

Free societies have prerequisites, and history has not given all peoples those prerequisites, which took centuries to evolve in the West.

And he concludes:

Political spin may say that Iraq has nothing to do with the war on terror, but the terrorists themselves quite obviously believe otherwise, as they converge on that country with lethal and suicidal resolve. Whether we want to or not, we cannot unilaterally end the war with international terrorists. Giving the terrorists an epoch-making victory in Iraq would only shift the location where we must face them or succumb to them.

Abandoning Iraqi allies to their fate would ensure that other nations would think twice before becoming or remaining our allies. With a nuclear Iran looming on the horizon, we are going to need all the allies we can get.