A number of possibilities.
One: Dangerous World Syndrome. You have to ask yourself--didn't this crap go on when I was a kid? I'm sure it did, but we never heard about it. So...is the world really more dangerous--are there really more child-abducting/molesting perverts than when we were kids--or is the 24/7 newscycle and Amber Alert just making us more aware of them?
Two: Sexualization of children. It's disgusting. I was at a strip mall the other day and I saw a little girl in a stroller whose t-shirt was labelled 'future porn star'. Really, I have to ask what kind of sick idiot puts that tee on their daughter? I went BALLISTIC at a male friend of mine who bought his then-thirteen year old daughter sweatpants with the word 'juicy' written across the butt. "What's the big deal?" he asked. Geez, just like every other pervert in the universe now has his eyes drawn to her butt and will say, 'sure looks juicy to me'? Nah, I don't see any problem.
Three: sexual submission/pornography. Yeah, 'scuse me whilst I hop on the gender-studies soapbox. Here's the problem. Real women aren't as...passive and submissive to male desire as women in pornography are. Guys who grow up watching a lot of smutty stuff start thinking some pretty awful things are okay, like...nonconsensual sex. Like your desire matters, and hers really doesn't and that she really likes it when you are kind of rough/demeaning. When said guy tries that with, say, a real woman and gets shut down...some of them decide that it's THAT obnoxious woman, or that they're too old, and they should 'get them younger' before all those 'hairy legged feminists' get to the girl and spoil her with these notions of subjectivity and dignity and such. Thinking that way, a young girl is pure and untouched and perfectly passive. With little boys, in Japan it's been enshrined as shouta but it follows the same basic principle. Young, and pure, and acquiescent the way older ones aren't.
Now this isn't just men: how many more stories do I have to hear about female teachers having sex with their underage students? (Excuse me

) Look: I teach, and my kids are technically all above the age of consent but the very thought of it....oh it literally makes me queasy. But apparently it happens--I asked one of my developmental comp students about it (we were talking about creeps on myspace and it came up) that every single one of them knew someone from their high schools who had had sex with a teacher. WTF?!?! We keep sexualizing young folks and this is going to get WORSE. I know those teachers aren't *abducting* the kids, but it comes from the same nest of symptoms and is, at least to me, almost as morally repugnant.
HK, Just think of Jon Benet Ramsey.