I don't think every Muslim expansion into Europe was for the sake of destroying Christianity, mind, but certainly they set the stage for religious as well as ethnic conflicts that fester even now. I think of Turkey as a thoroughly Asian country, but not all Europeans see it that way, and being at the crossroads does give some legitimacy to the idea it's equal parts European and Asian while being wholly neither. But the fact remains that until/unless Turkeys government conducts itself as a 21st Century democratic state, or its people compel the government to do so, it really has no place among such states. Making Turkey an EU member while it continues to ignore rather than reform its past does nothing to alleviate the Balkan problem that arrived from there centuries ago, and a great deal to exacerbate it.