I agree with DVK's position somewhat: we get into unmaintainable territory if we start enforcing a standard set of sources for answers. Every work has its own definition of "canon", if there is even a consensus (for example, some consider Star Trek: The Animated Series canon, others don't).
And what do we do if an answer is provided that doesn't cite the hypothetical list of acceptable sources? Do we go the route of Skeptics and put the onus on moderators to delete them? Less drastically, we can't force people to not upvote those answers or downvote them, either.
So like DVK, I agree that "what counts" is dependent on the evaluator: if you don't think an answer based on Wikia is useful, vote it down. If you're asking a question and you receive two answers—one from a source you trust and another you don't—accept the former. If you're up for it, maybe even dispute the claim based on the Wikia source and ask for better citations.
But I diverge from DVK in that questions do not have the right to restrict acceptable sources as sort of a backdoor way to this, where if an answer doesn't use the source the question states as valid, it's technically "not an answer" and should be deleted.
The main project here is to be a useful internet resource: questions answered here will potentially help anyone in the future who happens to be searching for information about the same problem. If I search for "Why did X do Y?" and find a question here with answers, the expectation is that that Q&A pairing is our definitive answer to that query.
But let's take the situation where it's okay to restrict a question to a set of sources. You have two situations:
- The list of acceptable sources for the topic is universally agreed-upon, making the restriction unnecessary.
- The list of acceptable sources for the topic is not universally agreed-upon, and the Q&A pair is not definitive.
In the latter situation, if I'm searching for information about the problem, and I don't agree with the question asker's set of acceptable sources, I'm in a real bind: the answers don't help me, and if I ask a new question, it's likely to get closed as an exact duplicate of the first one.
Ah, one might say a new question asking the exact same thing but with a different set of acceptable sources is not an exact duplicate! But that's neither sustainable nor in the spirit of the closure:
- Is having a dozen different questions asking exactly the same thing really acceptable? Five? Where do we draw the line? What happens if that line is less than the number of combinations of acceptable sources, and the extant questions don't help me?
- If I'm not a discerning reader, don't have a favorite set of acceptable sources, and search for an answer, what do I do when there's a number of questions asking the same thing with different answers? How do I compare them?
Instead, questions should ask about a topic or a problem and that's it. Like above, if you think the answer's sources are acceptable, upvote it or accept it. If you don't, downvote it and optionally explain why the answer's sources are lacking.
This way, what's acceptable is organically decided by the community (through votes) and the asker (through the acceptance check mark), but we still allow for a comprehensive Q&A pair should future visitors not agree with either.