A great deal of what happened in Germany was due to a certain kind of theological liberalism, and wasn't exclusively Lutheran. Both Barth and Bonhoeffer understood this. Liberal religion became intensely ethical in the name of social respectability, and this was interpreted as an imperative towards advancing the greatness of culture, and if the culture is antisemitic and nationalist, the religion becomes antisemitic and nationalist as well.
I'm trying to prevent painting the whole thing with one broad brush. WWII Germany was not a monolith - some giant being with Hitler as the head and all Germans as the body. It was a geographical area of millions of individuals - each with a different experience. A good historian understands this, and again, I can show you studies on how historians deal with just this problem.
So, yes, Germany was not a religious monolith of Lutheran orthodoxy. There were Catholics and Pietists and Reformed and the academic liberals and so on. But that doesn't mean Germany was without orthodox Lutherans - my father-in-law's family was very much Confessional Lutheran. And some of those "proper" Lutherans participated.
It was a chaotic mess. My wife's grandfather served in the German army during the opening invasion of Poland. After that he became somewhat of a conscientious objector, and was sent back to Mannheim to work in a factory. Given that he made material that supported the war effort was he then an objector or a supporter?
Since Mannheim was constantly bombed, he sent his wife and kids to live on a farm. There my wife's grandmother spent the war at near starvation levels, scratching out a daily existence, and late in the war had to fight off attempts from Russian soldiers to abduct her until the Americans arrived. How do you classify that nebulous middle existence where she neither resisted the war effort nor supported it, but only thought of surviving it?
As a Vietnam Vet once explained to me,
when one is in the midst of these horrors, all the military strategies and theological arguments go out the window. The "no atheists in foxholes" is both right and wrong. Not only are there no atheists, there are no theists. It's just a brute existence.
Well, as I pointed out, I don't think US Christians are necessarily all that faithful, either, or all that different from Nazi Germany in essence in their modus operandi of advancing a kind of "Positive Christianity" built upon the myth of being a "peculiar people". The only difference is we as a culture are somewhat less anti-semitic and we are a little more cognizant of the dangers of fascism. But as not-so-distant events have shown, such as in Charlottesville, Virginia a few years ago, memory fades, and what was once completely unacceptable has now become acceptable for a minority of young people unaware of history.
Again, I don't disagree there are many people who fit that mold. It's just that it's not all people. The hope is that such people will be prevented from making a big splash - though sometimes they do.