With Islam, waging war and repression comes directly from the mouth of their "prophet". Catholics are not muslims, they have a choice to do evil or good.
And Orthodox Christians have a choice too, and not all of them were as decent as the Serbs. Orthodox Christianity has its fair share of atrocities against Jews. Ever since the Russian empire and their Cossacks annexed Jewish populated lands in Europe they have been massacring and persecuting the Jewish people. And during the Holocaust, the Nazis had significant support amongst Orthodox nations, especially- In the Ukraine, Romania and the Baltic countries.