How strict should we be about references?
When someone makes a claim, should we require them to support that claim with a source? If so, to what extent should we go? Must all claims be referenced or just some?
Wikipedia has had a huge influence over the development of Stack Exchange. This is another instance where we steal page from Wikipedia's book. After all, why reinvent the wheel?
The Wikipedia community relies on the No Original Research core policy to combat unsubstantiated claims from finding their way into articles:
This page in a nutshell: Wikipedia does not publish original thought: all material in Wikipedia must be attributable to a reliable, published source. Articles may not contain any new analysis or synthesis of published material that serves to advance a position not clearly advanced by the sources.
The very purpose of this site, as defined by the FAQ, is to combat unsubstantiated claims:
Skeptics - Stack Exchange is for skeptics, rationalists, free thinkers, or anyone who questions pseudoscience. Skeptics is about applying skepticism — it's for researching the evidence behind the claims you hear or read.
The voting system of Stack Exchange is largely meant to relax any need for specific policy regarding what constitutes a valid answer (and by and large it accomplishes this) — however, due to the nature of Skeptics, the community needs to enforce the idea of no original research to encourage healthy voting.
Users are required to reference all significant claims they make in their answers.
There are some types of questions that we can safely answer without needing references, however, such as claims that blatantly violate some laws of nature or known scientific facts (around high school level). For example, debunking a claim about a perpetuum mobile, linking to Wikipedia's article about the laws of thermodynamics might be advisable, but only for the reader's convenience.