The federal government quite famously (briefly) regulated toilet seats a few decades ago.
Laws are not enacted/enforced to protect people from themselves. The only recent one I can come up with is that stupid-ass sugar ban in NYC.
Possession of child porn, for one. Have sex with a 14 year old?
You have to knowingly possess child porn. I can't go hide a picture of a naked kid in your wallet and have you arrested. And having sex with an underage is negligence. If under the (ludicrous) circumstances provided you were being charged, in all likelihood the grand jury would toss it.