You misunderstand me. I am not arguing against the law. Just against cultural bias.
If you left 12 year olds to their own devices without educating them that they shouldn't have sex, many of them will probably have sex. That is what I mean by "it is normal". Is it even illegal for 12 year olds to have sex?
Also, out of curiosity, how would you explain to kids that they shouldn't have sex? I think some reasons don't apply across all cultures.