If you cannot understand the Germans welcoming the Syrian and other refugees, consider that they are the children and grandchildren of individuals who executed the holocaust, the invasions of many nations, shelling of their cities, campaigns against partisans which executed very many civilians. For their Fatherland, for their German culture.
Those individuals knew they did terrible things, had to excuse themselves as being ignorant in the midst of mass insanity and going along with the crowd. But they knew and those still alive know what evil ordinary men can do when they allow themselves to harm others, and the ease of justifying that, and the ease of adopting opinions that naturally lead to those justifications.
That generation lived through the political events and propaganda which lead their nation to that state of producing such very great evil. They and their children have read endless analyses of the cleverness of the German propagandists, the step-by-step conversion of different groups to the increasingly insane policies, the bureaucratic infighting about %age of deaths desirable vs number of workers needed. And also, weakness of German citizens in independent critical thought, in the moral strength to stand up to peer pressure. All of which resulted in ordinary people doing great evil for ordinary-seeming reasons, at the time.
At the time, none thought the opinions were too extreme, everybody thought the same. At the time, the nation was obviously under attack by Communists and the WWI enemies were trying to keep the country down, those are facts, and justified the justifications. At the time, none thought they were guilty of anything, just doing what needed done.
There are dozens of discussions on Youtube, several different people with videos of their time at the Russian front, etc. Go explore, find that wisdom, it is a new resource for personal understanding everyone should take advantage of. No use repeating dumb mistakes of civilization, you know?
Those individuals, guilts ranging from people who did very great harms through people who did not object to the anti-semitic statements of their peers, very likely learned some wisdom from their lives. Good parents are careful to pass those lessons along. No use having your kid to bear the burden of such guilt, it is so easily avoided.
Germans living among us here in the Western world are no doubt investigating what country will be most insulated from the catastrophes they see unfolding. Germans know what happens when a country realizes it has a Jewish Problem.
It isn’t just the Jew-equivalent-of-the-current-hate who are in danger, anyone whose politics doesn’t fit the extremist-in-power-this-week is equally in danger.
Bad people will always be among us. Wisdom of the ages suggests that you not allow yourself to be one of them.
Wisdom of the modern world is paying attention to the propaganda, and realizing that your rulers will use your every hate against you.
Added later. This shows the situation for the average ISIS member is the same : local factors combine with beliefs under the control of ideology and propaganda to produce evil. So routine.