Yes, I know that the Church doesn’t teach that forced conversion is okay.
Well, yes and no.
Vatican II document on religious liberty is relevant for part of this Conversion issue. We respect the right of the individual to worship in the way he chooses.
But the Church also assumes the Natural Law, which provides broad parameters that influence some actions, as well as divine law.
World War II was often described as a “Crusade”. Countries like the US, which was then largely driven by Christian values and still somewhat respectful of the Natural Law, refused to negotiate a stalemate with Germany, which was under control of an ideology hostile to Christian values, and hostile to the Natural Law.
We sent our soldiers to invade a continent that had not invaded us. We broke the laws of Germany and its allies. We removed the legally constituted government of our (religious) opponents. We did not require the replacements be Christians, but did require that they not be Nazis. But no Nazi was required to attend church, nor were the new leaders.
So, yes, the Church did support this “forced conversion”. But no, the Church did not support the forced conversions of individuals, or interference with religion perpetrated by the Nazis.
Actually, the Natural Law had been somewhat undermined even in the US and Canada prior to the War. The atrocities committed by Nazis, who so blatantly opposed the Natural Law, led to a temporary period of respect for it in the West, now ended. They put the leaders on trial for crimes against the Natural Law, but they called it a compromise name, “Crimes against Humanity”.
Since then, Margaret Sanger’s support for some aspects of Nazism, and their support for some aspects of her program, have been mostly erased from the public memory.