I think what it probably comes down to is that it's the parent's job to raise the kid, and on their own time. If someone doesn't agree with their methods or time tables, it's none of their buisness. If a parent wishes to keep their kid sheltered until they feel their ready to learn about sex, that's their call as a parent.
To unsensor everything (I'm assuming you mean television, radio, etc.) would be making it very difficult on the parents to maintain what they feel is right. At the moment, if a parent wishes to wait to inform their child, they can do so with careful supervision. And for those who don't care what their kids do or learn, you could always pop in a porno and teach them to masterbate whenever you want. And if it's just an issue of wanting to enjoy shows or music unedited, it's easy to get that without turning on basic tv or radio. It's not like sensorship is making things harder on those wishing things to be unsensored.