Keith and Fred are both suggesting things that make Wiki not Wiki, but would work for a free online encyclopedia in the long run. Do we want anonymous editors spamming their URLs all over, or writing "poop" or "Andrew is gay" in major pages? It's not wiki to lock them out, but we're writing an encyclopedia.
I have recently seen numerous instances where anonymous editors have removed vandalism, often within 30 minutes (or even quicker) on pages that are not especially popular. This means several things. This means anons can contribute very constructively, but it also means that our traffic has reached the point that pages are served so often. I wouldn't expect every visitor to correct the vandalism (figure of 1:6 comes to mind). Therefore, every epidosde of vandalism is witnessed by countless visitors until a kind soul picks it off, either through RC patrol, a Wikipedian with the article on his/her watchlist, or said anonymous saint.
Fred is suggesting a para-wiki where arcticles are fact-checked before they go live. I would like to propose that as soon as an article reaches featured article status, it is semi-protected. Only registered users (or even registered users with a good track record) can edit those pages. Changes can be proposed on talk by anons and then be effectuated by registered users. This will put an editing funnel on our most prized content.
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