I'm sure some of them are harmless, but in some there are obvious mental health issues at play with people seeking constant validation over multiple threads, and this is without taking into consideration the fact that the OP may not be the person in the photos at all and is just using it as another way to bully or harrass them by asking strangers to critique unflattering photos of their victims.
You can't really say they're of value or provide an interesting discussion (almost invariably they descend into nastiness), and given the questionable motives for posting them I can't understand why they're allowed.
Is this something MNHQ might be willing to consider further in future? I know we've had a bit of a rash of these kinds of threads over the last few months.