I would go so far as to say that any open-source project that does not publish a manifesto tends towards dictatorship.
If I have a change I want to make, how do I know if it will be welcomed? Should I bother to submit it, or should I fork instead? If there are principles on which such decisions can be made, writing them down saves everyone time. If not, it comes down to the tacit opinions and gut feelings held by the dev junta, and the messy business of unearthing them.