CA, I was being sarcastic.
Avira,
1. And Yiddish doesn’t have kefira? The biggest kofrim were the Yiddishist Bundists. It also has improper words.
2. Rav Moshe (Iggerot Moshe Even Haezer 3:35 based on the Sifri (Devarim Piska 46) which is quoted by Rashi on the verse of ledabber bam (Devarim 11:19) says that it is a mitzva to speak in Lashon HaKodesh. In fact, this is one of the merits our ancestors had in Egypt.
3. Who says that baalei teshuvah are drawn to the “warmth” of Yiddish in a shiur? Perhaps they just find it cute and quaint. Like an old family heirloom that one keeps in the closet and dusts off once in a while. Not to mention the fact that it is very annoying and difficult to try to follow a shiur when one does not understand the language. This is why both Rav Soloveichik and Rav Yaakov Kaminetsky changed the language of instruction to English. BTW, in English “Yid” is a pejorative.