I posted two photos on the other thread and got some useful (to me) feedback, including some critiques that appeared to be thoughtful. I figured I knew what I was getting into, and was prepared for a bashing. But I don't find the feedback on Flickr to be conducive to improving one's photography (at least, not in the groups I usually post to), so being on the receiving end of more robust and unvarnished commentary seemed like an idea whose time had come.
That said, what I think the other thread revealed was that there is no consensus on RFF about what the substance and tone of a critique should be, whether "brutal," 'honest," "candid" or whatever. I think others posting above have said something similar.
Maybe the way forward is for members who want their photos critiqued to start their own threads, perhaps with a short statement about what they're trying to accomplish, and invite comments from other members, including questions about the photos so there could be some sort of dialogue (I like that idea). Anyway, my two cents.