Let's be clear. We are talking about whether one should "take wikipedia serious as a source" (emphasis mine). You invoke "source", too, but I'm unsure if your focus is on how reliably accurate Wikipedia is, or if you really do mean to say what you say.
Even assuming yours is the saner of the two--that your "trustworthy" and "credible" mean to say that Wikipedia is reliably accurate--well, I'll first note that this was not the topic at hand.
Since you've appealed to common opinion twice, can I presume that your own use of Wikipedia is also a typically casual one? That is, that you rarely if ever make a point to verify the claims made in articles by:
i) Cross-checking the cited sources, and/or
ii) Independently verifying things in some other way
If I'm permitted to make that presumption, then for my second point I'll note that unless you've done these things, the statement that Wikipedia is "trustworthy" and "credible" is a vacuous one.
I'll also note that I deliberately made a point of saying who's holding this opinion when I wrote that it's a "weird inference that has been tacked on by uninvolved bystanders following Wikipedia's success, and does not originate from within Wikipedia". There is, I think, a fairly realistic view of Wikipedia within the Wikipedia community, especially from those who were involved early. The "vast majority of the internet and wikipedia users" are not Wikipedia editors.
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To revisit the point I made in the edit to my initial reply to bugsy, I'll say that there's a reason every page on Wikipedia links to a page that says the following,[1] the formatting of which I can neither accurately reproduce nor adequately convey here:
> WIKIPEDIA MAKES NO GUARANTEE OF VALIDITY
> [...]
> That is not to say that you will not find valuable and accurate information in Wikipedia; much of the time you will. However, Wikipedia cannot guarantee the validity of the information found here.
