I grant you that some leftists are self loathing. In Greece we have Marxist Varoufakis. He not only supports the mass violation of our borders but the erasure of our very identity Far leftist like Varoufakis are trying to redefine Greek to mean solely a citizenship rather than a people and culture.. Varoufakis doesn’t apply his own alleged principles consistently though. He does argue to erase other people’s ethnic identities in a similar way. Just Greek.
Not every Greek leftist is like this though. It’s just a portion of leftists that behave in this self-hating manner. They are so motivated by their antinationalist worldview and try so hard to show non-Greeks that they are “antiracist” they end up bizarrely hating their own group. For a Jewish parallel, I’d argue long time Hamas supporter Normal Finkelstein is a self-hating Jew. Not Shumer who has a long history of supporting Israel against Hamas. His criticism is of far right Jews not all Jews.