Hi, Professor Paradox, and nice to meet you!

What GL_in_lyrics said in his response is quite on the spot. A few things I would add is that people in our culture have a love/hate attitude towards sexuality. Our society is still burdened with the relict belief from the Victorian era that sex is very negative. No matter how often you hear adults claim that they consider mutually consensual sexual activity for people of legal adulthood to be emotionally healthy and desirable, you will then see many people--often the same ones--turn around and express moral condemnation against specifically women who have many sex partners and enjoy expressing their sexuality, with pejorative double standard words like "slut" and "whore" (and many other synonyms that mean the same thing) directed at them. This proves that as much as people in our culture are obsessed with sexual activity and expression, and enjoy engaging in it, at the same time we equate this enjoyment of it with a lack of moral character--at least for certain groups of people, which changes through the decades.

At the same time, our culture is obsessed with the abstract concept of innocence. We are conditioned to view innocence not so much as an idea or concept, but as an actual state of being. This conception of innocence is simply a warmed over re-defining of ignorance, and our culture is so spiritually enamored of it because it's viewed as an inherently beautiful state of mind and being that is equated with goodness and "purity" of heart and soul; good evidence for this conflation of ignorance with innocence can be found in the popular saying, "ignorance is bliss."

In other words, if you know too much about the "bad" things in the world--read: reality--this is seen as deleterious to that awesome state of being. And since sexual activity and knowledge is one of the things our society views as inherently "dirty" and foul (no matter how much mutual pleasure it brings two people engaging in it), in order for someone--or some group--to be truly innocent and "pure" of heart and mind in our culture's eyes, they must by necessity be asexual, i.e., not "burdened" by the "complexities" of sexual knowledge and desire. In our modern culture, children--specifically, anyone under the Magic Age of 18, since adolescents under that age share a legal status with actual children--have been co-opted to serve as living personifications of that sacrosanct concept. The deep-seated guilt and sense of moral taint adults in our culture seem to feel over enjoying and indulging in pleasurable sexual activity appears to have spawned a psychological need for conscripting at least one group of people in society to represent the "purity" adults view themselves as lacking.

Since anyone under 18 lacks their civil rights and are not allowed to participate in the political sphere of society in our hyper-gerontocentric system, it's relatively easy to force 'underagers' to remain in a state of ignorance and disqualification from participation in the running of society that enables them to represent a semblance of "innocence" in our culture's eyes. It's certainly far more easy to enforce this state of affairs on anyone legally underage today than it is to force women into that role as was the case in the past, because women no longer lack the civil rights that youths under 18 were eventually forced to cede due to various social factors connected to the onset of the Industrial Revolution.

The conceptual paradigm of "childhood innocence" is every bit as sacred in the Western and Northern psyche of today as the notions of religion, Santa Claus, patriotism, tribalism, etc.