Who can opine? Who can critique/review?

A professional author said she thought only published professional writers should review. I picked her argument apart*, but it didn't change her mind (of course, I'd rather hear my literary heroes said, but sometimes their judgement isn't any better than Joe Blow's). Aparently, this phenomenon of presumed authority is circulating the web in multiple discussions. Here are two of the best:

Patrick Nielsen Hayden:
"The fact is that one of fandom’s defining characteristics (and World Fantasy Con is very much part of fandom) is that everyone gets to weigh in, without regard for formal credentials, professional standing, or membership in any particular class or caste. Indeed, the specific project around which fandom formed, in the early 1930s, was sorting out which stories in badly-produced pulp magazines were the good ones and which ones were crap. That’s the heart of the enterprise: not writers being supportive to one another regardless of the quality of their work, but readers separating the wheat from the chaff and sharing their findings with one another. This isn’t something you can do without ever being rude; at its heart it’s a process of discrimination and discernment that can’t be made unfailingly polite."

Dan Green (emphasis mine):
"It is true that not everyone's opinion is equally valid--but this means only that not everyone bothers to support his/her opinion with equal weight. Simply writing for a newspaper does not in itself convey a "true" authority to the critic, if the views expressed do not go beyond plot summaries and vapid opinionizing. Speaking for myself, I don't find much critical weight in the opinions--about either film or books--expressed in most of the "major dailies" The amount of space given over to reviews is much too sparse to allow for much real criticism of any kind."

*My refutation:
"Most professional writers should but don't want to review because they don't want to step on toes. They've established a career. Note that Jay [Lake] doesn't review anymore (to my knowledge at least). How does [one get] start[ed] on the road to being 'someone universally acknowledged as a grand pooh-bah of reviewing?'"