Leonard - if I've understood correctly you seem to be saying if teenage girls feel able to make the decision to start having sex when they feel ready we should let them?
If this is the impression you've got from reading my post(s) then unfortunately you have not understood correctly. So, sorry if I didn't make myself clear, and I'll try again.
In my opinion (based on experience) the majority of 14-year-old girls would choose not to have sex and therefore there is no need for parents to make that decision on their behalf, because the desired outcome (not having sex) is the same regardless. And, further, if a girl has decided for herself not to have sex, then shutting the bedroom door is unlikely to make her change her mind.
I also intended to point out that, in the case of those vulnerable girls who are not capable of making that decision, the solution is education, so that they know they have the right to say no.
And finally, in the case of the very few girls who genuinely are mature enough, and genuinely want to have sex at an early age (and I really can't see many falling into this category), then I concur with other PPs that they will find a way to circumvent any parental controls such as bedroom doors being left open/staying downstairs. Teenagers are devious.
I also agree with those PPs who suggest that it is pointless to bring up the "it's illegal" argument. So is any sexual activity - including snogging. But if you read my (long) post - written at the request of the OP - the government is aware and has made allowances.
So, I hope that clears up any confusion. No, I am not saying what you thought I said.