Prescriptivism rarely if ever creates useful linguistic evolution. The concepts have to change before you can stick new labels on them, or at least at the same time. And in this case what's being prescribed does not in fact tighten up any boundaries or "carve reality at the joints" any better than what it's trying to replace.
I once installed an operating system from a CD-ROM which I later learned through an Internet forum that I could have downloaded from a mirror FTP site and loaded as an .iso into the flash memory of a USB drive for LiveUSB testing of the Linux distro, a new flavor of Ubuntu.
Out of the 52 words in this last sentence, 22 of them were new or adaptations, commonly through prescriptivism, and a common enough list of words that one can find each of them commonly used on the forum you're reading.
I conclude that your assertion that "prescriptivism rarely creates useful linguistic evolution" is wrong. While I doubt Facebook will shut down to honor the "not sharing intimate non-consensual photos" policy (as it should... as it shares data including photos without informed consent [EULA doesn't count in my personal view]), they aren't wrong to call out the common terminology doesn't work for setting a policy as it is too vague.
Difficultas linguarum est ut evolvantur ad melius serviendum hominibus qui eas in condicione versantes loquuntur.