Board Thread:Reference desk/@comment-4028641-20121204012342/@comment-188432-20121218170628

What you ignore when you blithely combine the words "slippery slope" and "fallacy" is that some slopes are actually slippery.

It is a demonstrable fact on this wiki that allowing in some non-narrative sources does in fact lead to other non-narrative sources, of much lesser quality than the Brilliant Book being let in. I can point to hundreds of articles where supposed facts from things like Doctor Who: The Encyclopedia, various issues of DWBIT and any one of the written-in-universe-style of reference books have crept in.

The slippery slope is only a logical fallacy when there's a slope, but no ice. There's tons of ice 'round the notion of the non-narrative, BBC-licensed book being used as a valid source in in-universe articles.