Oh, nonsense on stilts. This isn't science, let alone a "fully scientific perspective." It's materialistic determinism, which more often than not destroys both liberty and reason. Just look at Marx's own materialistic determinism.
I think sometimes were are a bit too high-minded in our assumtions that we are so much in charge of our biology, as though it wasnt hormones behind the firing of every impulse in our brains.
So we aren't responsible for following or not following our hormonal impulses?
I think any look at society would suggest that laws are practically irrelavent when it comes to sex; some people will follow laws and some (most in my opinion) will not.
Can you name any of these societies? Even the liberal US doesn't allow kids to buy porn, and prosecutes those who distribute it to minors. That's certainly controlling sex. Why are you making a special provision for sex? Though it is a wonderful thing, there's no proof that it is in its own special category.
'Proper' is such a loaded word, because it is subjective, while positive is a bit more flexible and personal. i.e: you can pick my 'proper' from your perspective, but you would be hard pressed to pick my 'positive' which is a personal evaluation of the event.
Yeah, I'm speaking from a "subjective" perspective, and you're speaking from a "personal" perspective, and there's nothing we can do to change our minds at all, since reason is a myth. Why are you arguing, if you believe so?
May I suggest you read Professor George's essay The Clash of Orthodoxies? He takes apart what I perceive to be your underlying philosophy.