Criticism and advice are often wrong, but that merely highlights it is not a sufficient condition to becoming a better person, only a necessary one. Life is too short to learn everything by trial and error, so watching and listening to others is essential. A bias that critics are cretins leads to a life guided only by errors so great they can not be ignored, an inefficient path to enlightenment.
If Diogenes were out and about today, lamp in hand, I have a feeling he'd not say "I'm looking for an honest man," but rather "I'm looking for a sensible critic."
Criticism from any quarter gets a bad rap, in big part because there is so much of it which is just plain awful. It's one thing for everyone and his brother (and sister, and cousin, and the guy on the subway he brushed shoulders with last Tuesday) to have an opinion, but that just means the informed, enlightened opinions become all the harder to tease out and discern. It's hard for someone who's received a savagely negative opinion of their work to know if the negativity is just the reviewer, or if there is in fact a needle or two of truth buried in that haystack.
Very little work is done in teaching people how to compose good criticism; even less work is done in teaching people who to interpret it. Some of that stems from criticism being, up until recently, a relatively rarefied commodity. It's now easier than ever to find out what people think of something, but that hasn't made finding informed opinions any easier. The prevalence of five-star ratings on both Amazon.com and Goodreads is the biggest outwards symptom of such a state. It isn't hard at all to find someone willing to gush about X, but it's bleedin' impossible to find people who can talk about why X is great in a way that isn't just gut-gush.
Okay, so what to do about it? For one, anyone who is willing to call himself a critic should be willing to do some homework -- and by that, I mean educate themselves in what it takes to talk about something intelligently by way of examples from outside their bubble. If you review movies, don't just read other movie critics; read some Lester Bangs or, Conrad L. Osbourne's amazing piece on Luciano Pavarotti -- assuming you can find it.
Methinks that is half the problem right there. So much of this stuff remains so hard to find, so poorly known, that I suspect I'm going to need to devote a post to critical work that most pop-culture critics don't know about and could benefit from reading. Most people know who Roger Ebert was, I guess (god, does it ever feel weird to refer to him in the past tense), but have they read his 1992 essay, "Reflections After 25 Years At The Movies", which has more to say about the magic of film than most anything else I've read? If they haven't, they're missing out.
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