Europe has never been one. If you look at the history of Europe you see that it the EU consist of five zones who never before have all been united. The Baltic/North sea, Atlantic coast, Central Europe, Western Mediterranean and Eastern Mediterranean. Turkey is obviously part of the Eastern Mediterranean. They do have a different religion than what you find in the other zones but it is not more strange than Greece and its Orthodox church.
Demographically a poor country (Spain, Portugal, Ireland) joins the union around the time it has below replacement number of births. Guess in what fase Turkey is at the moment?
Politally it is a former somewhat racist and corrupt state that can’t admit its crimes against humanity so it is unlike Germany and .. (can you name another EU state because i can’t)
Economically poor states join as all the rich states have already been asked to join
Geographically, It is not like Cyprus (or Iceland) which have no part in Europe. Greater Istanbul is 25% of the population and on the boarder and if you claim that Kurdistan is in reality more a colony than a mayority lives in what is culturally seen as belongiong to the European continent. Besides nobody used this argument when half of France was in Africa(Algeria)

The US will not be part of the Union because it is to big. But i doubt that anybody would say no to Canada.

Bosnia, Serbia, Montenegro and Macedonia are an order of magnitude poorer and are politically a mess. In Bosnia you still basically have the national factions as political entities. In Serbia the ultra-right is very strong as is the support for Milosevic.

Regarding Croatia and Turkey, I don’t see really what there is to discuss. Croatia is geographically, politically, economically, culturally and demographically European by any definition. Turkey is partially geographically in Europe. Culturally, politically, economically and demographically it differs significantly from European countries. Sure, they helped form Europe over the centuries (mostly by invasion), but then again so did the Americans, and we’re not saying that they’re European, do we? Not that I’m particularly opposed to Turkey joining in two decades or so (after some serious reforms).

Pi.

Croatia has (as far as I can tell) one war criminal on the loose, but has sent others to the Hague. It is a stable democracy now and there are no widespread human rights abuses or threats of army coups. Its economy is relatively small and already fairly well integrated with Europe.

Turkey refuses to acknowledge any war crimes for anything (Armenian genocide, Greek expulsions, Kurdish ethnic cleansing, etc.). It is under constant threat of a military coup. The last soft coup was only a few years ago. It does not respect human rights, particularly freedom of speech and freedom from torture, and is only slowly moving in that direction. It doesn’t respect freedom of religion or minority cultural rights, and largely refuses to change. It occupies one EU member that it refuses to recognize and regularly threatens to invade other countries that it has disputes with (Iraq, Syria, Greece, etc.).

Let me use a different analogy for the two countries. Croatia is a smaller kid who was forced into a gang (Yugoslavia) after a lot of roughousing. It extricated itself with a lot of fighting under dubious leadership. Now it is trying to walk the straight and narrow but occasionally slips. Turkey is a bully that has beaten up all the other kids in the neighborhood, including its younger brother, Kurdistan. Partly because of this, the neighborhood is poor and unpleasant, so Turkey wants to transfer to a richer school in another neighborhood. But it refuses to improve its test scores, and it insists on fighting with people in the new school every day.

Why should the EU dis Croatia and allow in Turkey, Doug M.? And don’t give me this crap about stabilizing the Middle East. Stabilizing the Middle East is not the objective of the EU.

Indeed, or as in Yes, Prime Minister:
Sir Humphrey: Minister, Britain has had the same foreign policy objective for at least the last 500 years: to create a disunited Europe. In that cause we have fought with the Dutch against the Spanish, with the Germans against the French, with the French and Italians against the Germans, and with the French against the Germans and Italians. Divide and rule, you see. Why should we change now when it’s worked so well?
Jim Hacker: That’s all ancient history, surely.
Sir Humphrey: Yes, and current policy. We had to break the whole thing (the EEC) up, so we had to get inside. We tried to break it up from the outside, but that wouldn’t work. Now that we’re inside we can make a complete pig’s breakfast of the whole thing: set the Germans against the French, the French against the Italians, the Italians against the Dutch. The Foreign Office is terribly pleased, it’s just like old times.
Jim Hacker: But if that’s true, why is the foreign office pushing for higher membership?
Sir Humphrey: I’d have thought that was obvious. The more members an organization has, the more arguments it can stir up. The more futile and impotent it becomes.
Jim Hacker: What appalling cynicism.
Sir Humphrey: We call it diplomacy, Minister

http://en.wikiquote.org/wiki/Yes,_Prime_Minister

Yes, and isn’t that a reasonable position to take? Somebody has to stand up for the international war crimes tribunal, and investigation and prosecution of mass murder. By the sound of it that someone is certainly not going to be you.

What happens if (for instance) it turns out that Erdogan isn’t presiding (as I hope) over a party that’s a Muslim equivalent of Europe’s Christian Democrats, but is rather interested in making Turkey a liberal Islamic republic? Or, if the military decides that it has had enough and stages another coup?

From my perspective, undertaking negotiations on EU membership with Turkey now is somewhat like doing the same with Poland in 1989 or Romania in 1990. There’s certainly cause for optimism and membership is a good idea if it can be made to work. It’s just too early to be sure that things will work.