I went with my fourteen year old DS to the summertime ball at the weekend, and said to my DP afterwards that I wonder what we would have gone to see at fourteen which my mother would have cringed at. 
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Reality is that music is a generational thing and that every generation before cringes at the "music of today," not least because to them, most of it is shite.
But let's not pretend that the lyrics of the music of the 70's and 80's were pure shall we? Franky goes to Hollywood anyone? "Relax, don't do it, when you wanna come through it, relax, don't do it, when you wanna cum..." and the madonna video's - let's not forget that madonna was a prostitute who turned sex into music instead, ah yeah, fine example to set.
And the words to greased lightening "the chicks'll cream......".
As for people who believe that they protect their children from lyrics by not having them on in the house, you do know that they sing them in the playground instead? And that as they get older, if the message given out is that the parents don't agree with the lyrics then the parents will purely be branded prudes. Don't listen to shite music in the house by all means, but it's subjective, just because you don't like it, doesn't mean your child isn't entitled to...
People over-think this stuff far too much. We sang along to crap music in our teens, as adults we look back and go "wow, lyrics were a bit hardcore back then, no?" Or we laugh at the radio stations who banned relax, and all the other songs which were banned by South African radio where I grew up on account of them being imoral, but not before they'd already been in the charts and we'd learned all the lyrics and sang them anyway.