The left has never adapted to the transition from nationalistic wars to ideological wars. It took the left a while to grasp that the Nazis were a fundamentally different foe than the Kaiser and that pretending that World War 2 was another war for the benefit of colonialists and arms dealers was the behavior of deluded lunatics. And yet much of the left insisted on approaching the war in just that fashion, and had Hitler not attacked Stalin, it might have remained stuck there.
The Cold War was even worse. The left never came to terms with Communism. From the Moscow Trials to the fall of the Berlin Wall, the moderate left slowly disavowed the USSR but refused to see it as anything more than a clumsy dictatorship. The only way that the left could reject the USSR was by overlooking its ideology and treating it as another backward Russian tyranny being needlessly provoked and pushed around by Western Europe and the United States.
Having failed the test twice, it is no wonder that the left has been unable to come to terms with Islam, or that it has resorted to insisting that, like Germany and Russia, the Muslim world is just another victim of imperialism and western warmongering in need of support and encouragement from the progressive camp.