Whilst in many ways it really makes no difference whether Hitler was an atheist or not, or subscribed to "social Darwinism" - any idea can be corrupted and abused, after all - the fact is that there is no good evidence to support Stein's position. Worse, if one actually researched the source material - as presumably a reputable and honest journalist surely would? - one would actually find a great deal to support the opposite view.
In a great piece, "Nazi racial ideology was religious, creationist and opposed to Darwinism", Coel Hillier at coelsblog dispels this particular myth in no uncertain terms by doing exactly that and going to the source. With quotes from original sources throughout, the author neatly knocks down the lies that Hitler was an atheist or a Darwinist and, instead, reveals him as a(n albeit twisted) Creationist and Christian.
Does this in itself mean that Christianity or Creationism are bad? Of course not - no more than arguments about Hitler being an atheist or Darwinist would make atheism or Darwinism inherently bad if they were true. Let's face it, it was obviously plausible enough for people to believe it. Nevertheless, this is one myth I would love to see the back of. It would certainly be good to remove this particular attack strategy from the playbook of certain atheist-haters and anti-evolution lie-mongers; even if you don't understand the science well enough to appreciate the lies they tell on that front, this is a clear-cut integrity failure for all to see. (I think Godwin's Law is still safe, though!)