"Assuming Hitler was Christian though - wouldn't it be ironic that on one hand he denounced Jews as inferior sub-humans and authorized their slaughter, while at the same time subjugated himself to the King of Jews (Jesus) and recognized him as the greatest of all men!"
Firstly, I think that you will find that so called title, "King of the Jews" was a mocking one rather than than an acclamation.
Secondly, many Christians accuse Jews of killing Jesus so in their eyes there is no irony.
