The newspaper article says that
the pope draws a broad comparison between abortion and the Holocaust, saying both came about when people decided to usurp "the law of God."
Note it's a
Broad Comparison ... and note that what the pope is saying is that they
resulted out of a similar situation (people going against the law of God) and not that they were the same thing...
Not having read the book myself, it's not easy to make more comments, but based on the record of the Holy Pope, it's more likely than not that he did get it right & that Mr. Spiegel isn't.
I believe in the Pope's authority over the Church of God & his position as being ordained by God and that he is hence mightily annointed for his ministry.
Blessings,
Melody