All fair points but I'm not sure comparing the the daft things most of us did at 15 or so that probably only really put ourselves at risk can compare to joining a terrorist group that has very publically murdered people.
OK, yes a bit harsh .... but .... there's one of two possibilities in reality :
1. They are supposedly intelligent girls and they made the decision of their own free will. If this is the case then good riddance to them.
or
2. They were brainwashed. If this is the case then in all likelihood...
Couldn't give a toss about them personally - they're about to be sold into slavery if they go so go luck to them.
What concerns me more is that they must have been brainwashed here - by whom ? And why have we not detected their brainwashers ?