A "Wikipedia that allows everything". Try it. It'd turn to shit really quickly.
People seem to have this idea that there was this golden age of Wikipedia where you could write everything, and then the EVIL DELETIONISTS took over. The fact is, huge amounts of what gets put up on Wikipedia is junk. Deleting it is a service to the reader in the same way anti-spam filters are to email users.
Articles need to be maintained. To be useful for readers, they have to be reasonably accurate, and in Wikipedia-land, we base accuracy on external sources. And if there aren't any external sources, how the hell can we even try and be accurate?
Fortunately, there is a solution: the rest of the web. Wikipedia has a constrained mission, namely the production of an encyclopedia. Outside Wikipedia, there is a big wide web where you can do whatever you like. Wikis that have explicit points of view, that are focussed on specific topics... all that kind of stuff.