I really do think that the only way people will not say "but $reason means it's alright" would be a blanket ban. As this is not about to come from our community, which is very fractured over this issue, it can only come from above.
Is it technically possible at the moment to prevent images marked as fair use (ie, with a fair use template) from being used in user space? If so, is there a good reason for not enforcing that?
I suspect it's not possible because images are marked by using templates rather than, say, categories, but that could fairly easily be changed, no?
Steve