1.) Your enemies can use them to pinpoint your location
I hope he was making duckface.
On a more serious note, one hopes that it won’t lead to, say, “terrorists” posting selfies of “ISIS Headquarters” (a disliked neighbor’s house, or a restaurant where they got served a burnt kebab).
They can also make you look really stupid: https://s-media-cache-ak0.pinimg.com/736x/27/eb/1a/27eb1a7a8ad977ce758017a6e077f1a8.jpg
I don’t understand - do most guys use their left hand as a girlfriend?
Sure, sometimes. When I want to change it up.
Bigamist.
No, most guys use their right hand. Unless they invited a stranger over.
No, ambidextrist. 
Or ambidextryst. 
I’m a little surprised this story was released. Seems like exactly the sort of thing we’d like the bad guys to keep doing, and then see how long it took them to make the connection between “selfie” and “BOOM”.
I thought about this a little. ISIS’s way of recruiting, both for cannon fodder to come there and for home-grown hopefuls is through social media. If they stop so doing, it could be detrimental to the cause.
Thinking more, well, okay - maybe not selfies. Also, there may be propaganda value for our side in letting the world (and potential recruits) know the kind of brainiacs that can be found among their ranks.
This takes doxxing to a whole new level!
But most people know all about this. On a cannabis forum I frequent people share pics of their grows, but are careful to strip all metadata. If a bunch of stoners know to do it, you’d think a terrorist would as well.