I can see FB user turning all those recognition features off, but yet when FB is given a photo and asked by LE for help with finding you in FB network, FB can choose to comply with that and quickly find you in a stack of 100 billions of photos, providing LE with array of all your photos organized by time and place.
edit: also, I believe there will be more way of abusing photos recognition in the future. Just like Federalies are using Google Earth Maps to find who has a swimming pool and match this information against resident's taxes (whether they paid pool taxes or not) and acting accordingly if they haven't paid, I can see IRS tapping (or at least wanting to tap) into FB photos stream and find folks that bought luxury stuff and did not claim it tax-wise.