The past two hundred years have seen a flight from reason. Why? Because reason leads inevitably to Judaism and Marxism.
Marx's father converted to Catholicism, as did many German Jews, in order to advance his career. The Jewish mind is impervious to such pragmatic initiatives. 
Marx's essential Jewishness is not in doubt. 
Here is how one writer described it recently:
...
Marx is one of the great voices of Judaism. Many of Judaism's greatest voices were renegades from orthodoxy, Jesus and Spinoza, for example. Marxism is the full maturation of Judaism, its development into a full and explicit universalism.