There's no scientific evidence on this point of which I'm aware. In fact, an interesting argument could be made that the music is so engaging that people might be less likely to pay attention to the fact that they've been cut off. We just don't know. Research needs to be done on this topic. The lack of manners by people of all ages really concerns me.
Children learn from their parents and many parents today have very poor manners.
We don't know for sure, but my impression after having studied the American scene for a long time, is no. Yes, I agree that there's been a coarsening of our culture and a rise of ill-mannerdness, and we all have to be concerned about that. Families don't spend enough time at the dinner table talking about such matters. In fact, it's been argued that the American family dinner hour is disappearing. Many families have TV on during dinner.