On the Skeptics SE site we require that any claim be referenced.
To have a look at our requirements please check Guidelines for Inadequately Referenced Answers
Anecdotes and unproven general facts should be the enemy of this site as we are seeking to make the internet a better place by providing facts. If people are claiming something to be a fact and it is not supported by a reference then you are at risk of producing more internet lies which devalues this site as a whole.
By making references to claims necessary you avoid people saying anything they like.
I propose that we make this a policy of the site and start providing comments to users on unreferenced questions that they need to provide a reference to all claims on this site as it is the policy of the site to do so.