Your point is well taken, @Rarebear . I have been disconcerted by some of the advice given in my area of expertise, women’s health care. Jellies try to be helpful, and sometimes offer outdated information or give advice that has more to do with their personal experience than on science or research.
But your original question was asking opinions about doctors who give diagnoses and treatment online. None of the “peanut gallery” on that appendicitis thread claimed to be a doctor. When @shilolo weighed in, the other posters did not argue with him, they were happy to have his expertise.
Similarly, I have felt welcomed here on Fluther when I’ve shared OB/GYN information. Sometimes I preface my comments, with “I’m an NP” so jellies know where I’m coming from. I also try to provide good quality links to support my assertions, so that anyone with questions or doubts doesn’t have to just take my word for it.
I think the take home message is to consider the source regarding online advice. Not just medical. And part of assessing the advice is to take a closer look at anyone claiming to have expertise unless you feel you already know them well. Look for consistency and don’t hesitate to ask for sources.