Why is everyone on the Internet encouraged to be an expert?

Sites like this one, WikiPedia, and many others encourage everyone to be an expert, with no vetting at all. While a dairy farmer may also make a good dentist, I'm not sure I would trust him for the care of my teeth. Has anyone thought through the consequences of an Actor with a part-time job at Friday's and an associates degree in business providing mental health advice over the Internet?
 
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