Now, if someone's into BSDM or whatever, that doesn't really bother me, but promoting these ideals to young girls does.

That is very much my problem with it, although I think that the image and the nakedness and the boob job all factor into it as well as the lyrics and titles. Continuing the Madonna comparison, whereas Madonna's deal was more about being powerful and being in control, Britney seems to be saying she's property of whatever guy she's singing about. Those messages, combined with the slutty presentation, make what I think is a rather questionable impression on kids.