are many reasons behind this but the most suitable one i found that is-
When Germany lost World War I Hitler was
heartbroken, he claimed that the jews had stabed Germany in the back. He
promised to fight back and take revenge from Jews.In a book named Mein Kaimpf
Hitler had used many sentences for Jews and one of them is-"Conscience is
a Jewish invention; it is a blemish like circumcision"