Same problem arises with any song that's crap. Mostly people pick up on the body language and so forth. Maybe the thing is to find a way of pushing them in the direction of songs with a religious content that are not crap (such as "I bid you goodnight"). Same with politics.

Dealing with any kind of bigotry from a friend, I'd assume it's just thoughtless, and talk about it outside the immediate setting maybe. If that doesn't work, the frienship is in danger.

If people insist on giving overlong introductions I don't think its rude to ask them to get a move on and sing the song.