No doubt, immigration will present problems, I just don't buy the sensationalism about "Eurabia" and whatnot.
Although we tend to praise mixing as purely good, we often forget that mixing is a leading factor in leading to strife between communities. One example was how the most violent fighting in Bosnia occured in areas with the largest rates of inter-marriages.I have no problems with this happening really, cause I think mixing is good,
There's even a recent study showing that one reason why peace has prevailed for so long in Europe following WWII is because Europe's nations became more ethnically homogenous as a result of the war. Prior to that, there was much more ethnic mixtures and that lead to plenty of tensions and wars(WWI and WWII especially).