alt Hacker NewsWikipedia’s strategy is to offload the risk of wrong information to sources which can absorb the hit rather than have it reflected back. It’s “safer” for Wikipedia even to knowingly publish inaccuracies or misinformation from a reputable source than the truth from an unknown source. A lie from a reputable source is unavoidable, a lie from an unknown source is unforgivable.
It's also that letting editors argue based on their own original research would be a recipe for chaos.
"Use reliable secondary sources" is a simple rule that limits the scope for possible conflict and chaos. For an online encyclopedia that anyone can edit, that's very important.