Lithuanian Jews were mostly Orthodox. The assimilated liberal ones were mostly from Germany and western Europe. Poland was maybe half and half.
Suppose we had taken in a married couple from China who had fled the Nanking massacre. Suppose they had been very grateful and pro-American. But their son grew up to be an anti-American journalist who never missed an opportunity to accuse our nation of the vilest crimes. If that were the case, his parentage would be a relevant point for discussion.
Michael Moore was born into a typical white bread family in the suburbs, so nobody makes much of a deal about it. Not because of racism, but because many Americans of long lineage take our freedoms for granted. But if someone is an outspoken anti-American, and their parents came here seeking freedom from oppression, and were welcomed here, it's a relevant point because it shows just how despicable the turncoat is. He, of all people, should know better. And if his parents were conservative and pro-American, he's betrayed them as well as his country, and is even more despicable.