Regarding the "bias" thing, I can see how, in some cases that are not handled properly, it could come across as dishonest, if that's what you're getting at, OP. If the thread first starts with a "Mary and Sue went to the mall" thing, and then later the poster dramatically reveals that SHE is actually Mary, with (so it seems) the intention of getting direct sympathy, I can see how that might leave a bad taste in someone's mouth. Or if the responses are all like, "Mary was RUDE!" and then the poster says, "Well, I'm Mary, and here's additional information explaining why I acted that way so actually, I wasn't rude"... Again, that can come off as disingenuous or at least, poor storytelling.
IME, that's not how the majority of hypothetical --> true threads go, but I could see how hitting just a couple of them would make someone wary of others.