The issue is "how" can a culture allow something like Nazism to come to power. The problem is that Nazism was only the latest meglomaniacal concoction of that ilk in the Euro-sphere dating back 1000 years.
I actually realized the answer to the Nazi question about 5 years ago as I watched the Euro folk cede more and more of their soverignty without question with only the promise of a greater self esteem as re-payment.
You see, a gene pool which prefers to weigh the validity of opinion rather than one which weighs the validity of facts will periodically (like clockwork) succumb to these "greater-than-themselves" collectivist tendencies. Individualists rarely do. And there will always be a meglomaniac in the Euro gene pool who is more than happy to lead the wandering herd.
To a Yank, the idea that the "rise of the EU" should be welcomed because it will prevent the next intra-continental covetous property grab is tempered by our common sense understanding that the same mutant genes which produce the periodic Adolph Hitler will simply find another who will migrate to Brussells, bark to an adoring herd, and find new neighbors to menace. It is the genetics. It is the culture. It is enevitable.