Interesting topic, not discussed often enough. I tell you, I am about to abandon certain other nameless photo sites because the critiques there are as useless as some of the work posted. Rule there seems to be if the [nude] models are comely enough, it must be a good photograph.
I agree that part of the problem is people wanting to "be nice"; but also the problem is ignorance about what constitutes a decent photograph--the historical standards by which photography has long been judged. [Heaven help me, but do I sound like an old CODGER here or what?] If you don't know that, how can you offer anything much of meaning? On the nameless sites I haven't mentioned, it's either one big mutual-admiration society, or it's the anonymous tantrum-throwing low-rater seeking revenge for childhood traumas!
Too many people misunderstand the word "criticism", taking it to mean derogation; its actual meaning is revealed in its ancient predecessors: L criticus, G kritikos, "able to discern". People lack the knowledge or confidence to make the judgments required in discerning, in "criticizing", so they offer esteem-building platitudes which in the long run harm the critique-seeker truly hoping to improve his/her work.
My approach is to take the critique-seeker at his/her word when I'm told "critiques welcomed", or "tell me what you really think". I praise the praise-worthy aspects, and explain myself when I point out shortcomings, figuring if I can't do that then I'm not critiquing, merely spouting nonsense. I don't worry much about hurt feelings, because I assume the poster is a big boy/big girl, wanting to get better; because I don't attack ad hominem; and because the poster can read and decide for him/herself whether or not I'm FOS.