The problem with this view is that it doesn't tell the real story and no-one will ever know the real story. Adults, especially adults in positions of trust, are able to mould children's behavior in many, many subtle ways. It is easy to imagine a sexual predator who is able to persuade children to take the first step every time, and wind up having the children believe it's what they wanted. This is just as true of teenagers as it is of younger children--if you don't know that, you haven't spent enough time around teenagers. It is very easy for a charismatic adult to manipulate a teenager into doing pretty much anything.
Everyone knows that adults can manipulate children this way, the law knows it too, that's why there is a clear bright line around the age of consent, one that is raised considerably for people in positions of trust or authority.
Moreover, children frequently make bad decisions. The law doesn't allow a child to sign a contract, for example, for the exact same reason why a child can't consent to sex with an adult--it may be what the child wants at that moment and still not be in their best interests.
