> I understand why Yiddish speakers would not want to believe Yiddish is Germanic.

I don't think there's any controversy among Yiddish speakers that Yiddish is primarily Germanic. This is a recurring theme in Ashkenazi literature: Yiddish is understood to be the מאַמע־לשין -- the mother tongue, essentially grounded and practical, in contrast with Hebrew.

(Yiddish speakers might find the (non-joking) assertion that Yiddish is just broken German offensive, however. Or similarly, that Yiddish's non-German components are somehow less desirable than its German ones.)