Well, if sex were ONLY about "biology" then I would agree with you. But that is stripping it of its social, cultural, and political meanings. The fact is, thanks to things like the Disney channel and MTV and a host of other entities, our children ARE deliberately sexualized at a very young age.
When I see the 6yo girl next door in a pair of short-shorts with the word "hottie" across her butt I know that our children are being targeted. The quicker we get them knowing about sex, interested in sex, viewing and buying things that buy into the whole sex culture... The more money companies make.
I will not push my children into that world before they have to be.