Regardless, if it wasn't for facebook it would be happening on flickr or instagram or any other sharing site.
The problem is a legal one, not something that facebook can simply add as a feature. (Though they do have a way to report a photo in addition to untagging it. And then you explain why that photo violates privacy laws. https://www.facebook.com/help/?faq=217091804975136#How-do-I-...)