I'd be generally in favour of Turkey joining the EU sometime in the next decade. The whole point of the EU (as I see it) is to promote human rights, secular democracy, and economic progress - this has worked well for most countries, including Spain, Portugal and Greece, and the rest, so it shouldn't do Turkey any harm. It's true that they probably still have some way to go on the issue of human rights (laws against publicising the Armenian genocide, the Kurds, use of the army to "defend" the constitution) but I don't think that's anything unsurmountable.
Some of the arguments against which I particularly dislike include the one about the Turkish being "too culturally different" from the rest of Europe - I assume the main thing people mean by this is Islam. This is a load of chauvinistic bollocks - as long as the government is broadly secular, then what religion (or none) is practiced by a nation's populace is neither here nor there.