Peter,
I guess if I was you I would just listen. You know, to be fair, yes there are dangers on the internet, especially for kids. And in that way, I agree that facebook and other sites can be dangerous. But like all dangers there is a balanced way to handle it. The WT way is to say "Stay away from it all!" I tend to think they are strong about all of this, not because of the sexual dangers for children, but because of the "danger" of reading things contrary to their view. I can't say for sure, but that's the way it looks to me.
The way to handle these dangers is not to forbid access to these things, but to teach your kids well. They should know how to spot a predator. They should have good morals and values. But in the end, the internet will not be stopped. I was forbid to date growing up. But I snuck all over the place and did it all with alot of girls. That's the way of kids. If you forbid something that is naturally going to happen, they will find a way around it. Lock the door, nail the windows, it won't matter. So teach the kids well.
Also teach them to be open thinkers and to be intelligent. The reason many kids can be taken advantage of by predators is because the only things they are taught come from the WT, and that is pretty shallow.