I had a very sad experience back in SG-1 fandom with a person who I knew slightly on LJ and for whom I beta'd a story. It was a good story with good writing and had very ordinary issues with pacing and characterization that I pointed out, as beta's do, and this triggered a back and forth with the writer over email that consisted of them trying very hard to make me acknowledge that they were a failure as a writer, the story was a failure and that their writing sucked and that should give up. Nothing I could say got through to them.

Your post made me remember this. A very bad case of imposter syndrome. They were really suffering and it made me feel so bad for them. I learned that at that time they had approached several people I knew in that fandom for betas, seemingly with the sole purpose of getting validation that they sucked and should stop writing. Which was objectively NOT THE CASE.