I agree that they should have respected him enough to talk to him in earnest about his intentions with their daughter rather than go this far. Too late for that, though.
As for going this far however, which it has, I agree with Neutron. Whether or not it should have happened doesn't matter. The fact it did is all that matters now and the fact is not only is it legal, but theres nothing morally reckless about it. Their compassion for their daughter may seem blinding in the opinion of some of you, but it's a rightious compassion and anger all the same.
They are right to distrust him by virtue of this website alone. We are complete strangers who are influencing him one way or the other. And what influences him, hypothetically, influences their daughter (into adult/sexual situations herself), they may think.
Did any of you stop to think that maybe its not only him and his feelings they don't trust, but just as much their own daughter's? Think about it.
Whether its all on him or all on her or both, the parents may have made the accessment that neither of them is ready and/or responsible enough with what they have already, in addition to what they've learned of. And did anyone bother to ask what his parents think of the relationship in general? Age doesn't matter squat in these affairs. It's just a number.
I focus on the parents in this post rather than the action itself because if I were in this situation I would want their blessing, not their wrath. What has happened doesn't matter now. The relationship between the couple and the parents (both sides) can still be salvaged and not all is lost. He can still prove himself worthy in other ways of their trust, even after this. In fact, if I was the parent, I'd be appeased and impressed by his effort to try.
If I were the parent I'd listen to him (even if I had reason to suspect this may very well be nothing more than a puppy love crush), even after I found out about this place. In fact, I would even more so want a meeting with him so he can explain himself and his intentions with my daugther. I would want him to explain this fetish to me to and how he figures my daughter into it. What you people will have thought of whether I had a right to ask/demand or not wouldn't matter, because this is between me and the boy. Not me, the boy, and you. And it is only this way because I love my daughter and won't just hand her virtue over to some guy I don't even know.
Fate has dealt this hand. It can be worked through and still be fruitful if both sides play their cards right. The parents can adjust to his quirk so long as he can give them confidence in his ability to keep it under control around their daughter.
This situation is only as dire as it is made to be. It may very well be a way toward bringing the people involved closer. There may be fights and arguments to come, but if everyone can come to terms with eachother and eachother's feelings and respect that, then this negative can become a positive and they'll all have a laugh in the end, figuretively speaking.