Consistency is not a virtue of the left. Their reasoning is primarily emotional and rhetorical, so flat-out contradictions don't even give them pause. As you note, the Communists have made a fetish of the so-called Palestinians, an identity that was made up in 1979, based on a kind of thinking that is alien to the Arab mindset. The PLO was just an extension of the violent red brigades that came into prominence in the late '60s, and so the far left in the rest of the world made common cause with them. The victim-posturing and utter rejection of Western culture held by the Islamic world is music to the nihilist left's ears.