I mean the same things that people fault about Wikipedia can be said about scientific papers, anyone can write a paper and have it peer reviewed and approved. Isn't Wikipedia better cause it has a much larger audience that can call bullshit on articles of questionable factuality? Why do educational and research institutions frown against quoting Wikipedia as a reference? I mean some people even find information on Wikipedia and quote somewhere else just to avoid this.
During my university studies, a few classmates decided to edit a Wikipedia page for a niche technique in our field - changing the article to state it was invented by a rather boisterous member of our group.<p>The year following our graduation, my classmate heard from the tutor who runs the related course -- asking why the hell his students were claiming he invented such-and-such technique! Several students had cited Wikipedia without checking sources.<p>To answer your question, Wikipedia is a lower quality source than scientific journals for the same reason direct democracy isn't usually as good as representative democracy. We delegate trust in matters to an authority. Sometimes there are problems with the quality of the authority but at least there is a framework to work within.
It prevents circular referencing. For example, Wikipedia might be referencing Legitimate Science Page, which references Science R Us, which references Science Experts Coalition, which references Wikipedia.
It's because Wikipedia is edited by anonymous people. sources is not to say "this is true because this is written in this source" but "this is true because someone <i>with authority</i> said so". Citing sources is is a form of argument from authority. It is a a fallacy if the source has no authority but a completely valid argument if the source does. Wikipedia has no authority because of its anonymous nature. There's no one to hold responsible and no one who'll lose credibility by publishing bullshit on Wikipedia.<p>Also, most Wikipedia articles worth citing contain really bad factual errors. Since most readers aren't topic experts they don't notice such errors. But they are there and they are really bad. I only have some math education but I've found lots of mistakes in proofs on Wikipedia. Imagine how bad it is for higher-level math that is beyond the reach of most visitors to the site.
On overall I agree that having a larger audience is better for WP.<p>But most WP users are quite passive, and unfortunately a very few are extraordinarily active, so the quality of the WP they patrol, depends heavily of their biases. As they are few, there is no natural moderation.<p>But having a quality article is not enough, it is also important to have quality articles on a reasonable range of topics, and this is not true for some WP (French WP for example)<p>Same article since 2012 about cancer vaccines, only 42 words!
<a href="https://fr.wikipedia.org/wiki/Vaccin_contre_le_cancer" rel="nofollow">https://fr.wikipedia.org/wiki/Vaccin_contre_le_cancer</a>