The crux of this story is that David Letterman thinks sex jokes about 14 year olds is an acceptable laugh line in America. Since he’s one of America’s experts about what America thinks is funny, I can only assume he is correct.
Angels walking in pairs should scare the bejeebers out of knowledgeable Americans, of whom, I hope they number more than 9 per city.
As Christians, we would not accept what he has said or done as sufficient; however, for the (non-)man he is, this is it.
As for intending to use an 18-year-old as the recipient of such a joke (I'll grant his writers leeway on which daughter because they didn't mention the daughter by name (as they have in the past) and I thought it was Bristol with Sarah, as well), it was definitely wrong, but public figures and their families have to deal with this.
It doesn't mean we have to watch or support the advertisers of such a show. I haven't been able to stand a complete show of his for over a decade for his liberal bent, alone.