Your lack of understanding of canon law does not have bearing on the subject. Hitler was no longer a Catholic so excommunication was not necessary or appropriate. Luther, on the other hand, represented himself as a Catholic and was excommunicated, not for writing a book, but for his heretical advocacy.
I lived and worked in Israel for several years. During that time I witnessed a good deal of racism and prejudice by some Jews towards Arabs, Christians, Germans and even Ethiopian Jews. Some of these were governmental figures and others prominent in Rabbinical organizations. I do not believe that these positions, even when justified by Scripture, were indicative of Judaism, Israel or Jews in general. Do you?
Natural Law:
It is also the case that Martin Luther at the time before his excommunication was Father Martin Luther, a priest of the Augustinian Monks/Order, and he was challenging the 1,500 year apostolic Tradition.
Excommunication is incurred 2 ways 1) ferendae sententia, which is after a formal proceding, which is what happened to Luther and 2) latae sententia, which is an automatic excommunication because the act itself is a serious rupture with the life of the Church and thus Christ.
I don’t have a 1917 Code of Canon Law but at that time, there were some 30 offenses and under the 1983 Canon, I think there are 7, 1 of which is procuring an abortion. Another one is Apostasy and heresy, which certainly Hitler would have been guilty of. He clearly viewed Nazism as a religion were the German Race was superior to non-Germans, note he invaded Poland and killed thousands of Catholic Priests there and viewed the Slavic-Poles as subhuman.
He publicly claimed that Jesus was the “bastard son of a Roman” Soldier, thus not Jewish. Again, Heresy and Apostasy,
Thus, under canon Law, Hitler was excommunicated latae sententia. End of discussion.
How convenient, what happened to ´"Once a Catholic always a Catholic," upon which you base your gazillion followers world-wide. Is that to lie to inflate your following?
Once Baptized always Baptized. You cannot undo your Baptism. Baptism makes you a Christian and member of the Mystical Body of Christ"
So when Hitler was baptized into the Mystical Body of Christ in the Catholic Church, it was only provisional, until Natural Law discovered canon law to say it ain't so.
Is it true that a Catholic remains a Catholic and subject to the laws of the Catholic Church, even if they do not practice the Catholic faith, unless they have formally left the Catholic Church?
Not that it matters because Pope Pius XII was also Hitler's good friend and beholden to Mussolini for making him a Head of State. Such favors are always rewarded.