You just conceded that parents cannot explain 100% of the variance in how kids turn out - that society does in fact have some influence. With devoted parents that influence is smaller, but you can't shut it out completely. As another poster pointed out, even Amish children know who Madonna is. So your choice as a parent is to socially isolate your children, or to allow some exposure to society at large. Christians are already criticized for homeschooling their kids - they are being poorly socialized for doing so.
Society will never be "perfect." Bad influences will always be out there. It's simply the cost of living in a society. Giving government more power to make society "better" will, in the long run, rob us of our freedoms and make the situation worse.