I'm pro contact in cultures where it's accepted - either hypothetically or real-world past (most likely) cultures because there's no reason why it would cause harm there, and no evidence I've come across.

Today - I think it would depend on the culture to an extent. E.g. I think that having sex with a child in an English-speaking country - where the attitudes are worse than anywhere else - would produce the highest chances of harm for the child, and I couldn't condone it or practice it. Other places where attitudes aren't as bad - it would still be very ill-advised, but I think that there's probably a much lower risk to her if you did become sexually active. It is low enough to be ethical? Maybe, I don't know.

Unfortunately no one's really researched the above, so I can only speculate.