It's interesting that one reason the Dutch study cites that accepting teen sex can be good is that it promotes monogamy. I honestly have mixed feelings about teen monogamy. It's not that I think running around and serial screwing is great. But I grew up in a rural religious culture where it was common for teens to develop a relationship that was essentially like being married, and I don't think it was super. It looked a lot like the kids owned each other, to be honest. It's so natural to be interested in many different people especially when you're young and it's all brand new, and yet the rules were very specific that once you make a contract to go out with someone you're doing something very, very wrong to be interested in someone else. Very often they'd have a first or second boyfriend at 15 and literally marry the same person after a few years together. It was quite territorial, and it made me uncomfortable.
I guess I just don't see monogamy as an independent value of its own like kindness or honesty. What I'd like to do is teach my kids honesty, good communication, ethical treatment of others and safety. Those things can be present in relationships of any duration or kind.