That's an absurd assertion. Is constructive criticism appropriate or are only panegyrics allowed as comment?
there isn't one. if you don't like fan-fic, don't post on the subject. you'll not be appreciated here and none of the other forums are appropriate.
Yeah, right...I think you need to redefine 'constructive critisism'. Want to make constructive comments about individual stories, no problem, however you seem to just want to make stupid sweeping statements about the entire range of fanfic.
Why is fanfic useless to the aspiring writer? Why does the fact that I write stories featuring original characters in the Trek universe make them less valid than if I wrote original characters set in a historical setting like WWII?
Your argument has no weight.