You could have said the same thing in Germany in the 1930s about parties opposed to the 'alien cuture' of Judaism. Do you honestly think that it was a good idea then for German voters to support National Socialism, to defend against this 'menace'? Do you honestly not see that the situation today is almost a perfect parallel to the situation then - with the significant difference that the German supporters of National Socialism had the excuse of not having seen where this attitude leads?
I expect that the anti-immigration parties in Europe will also make the trains run on time, and give people back a sense of pride in their nation. History tells us that this is NOT a good thing.
Anyone familiar with American history knows that your generalization is bunk, unless you are saying that Germans are a "special" breed of people prone to renewed genocidal ideology. Is that what you are selling?
If not, be reminded that the US has had periods of highly restrictive immigration without a resultant 'fascist' regime. For example, the 1920s legislation that ceased the turn of the century waves of eastern and southern european, and Chinese immigration to the US. Half a decade later FDR became President.
In the early 50s, President Eisenhower cleaned out millions of illegals in Operation Wetback, reasserting border control.
Rather, what history constantly teaches us is that when a nation is subjected to vast numbers of foreigners, especially within a shorter time frame, a great many harms are visited on the well-being of the native population. The mass migrations of tribes into the Roman territories, the mass migration from Europe into the new world, the Jewish return to Palestine, the British migration to Australia, etc. .
Germans, for generations taught the shame of fascism, are stripped of their moral authority. Apparently they feel compelled to pursue altruistic policies, even if it results in significant and permanent harm to native Germans. Fortunately, there are other Germans unwilling to let their identity, culture, social, and economic well being sink without a fight.
I can see little reason for Germany or Sweden to accept and support a permanent underclass of millions of migrants...other than to avoid (German) tutored pathological guilt.