Let's pretend I did a stellar job at making The Co-Writers and everyone on the planet started developing a deliberate writing habit: how would it impact the world?
The practitioners would start thinking more independently and become proactive. We would know ourselves better, so we'd be able to fulfill our needs more efficiently and provide concrete solutions to our deep-rooted issues. Change would come from within and naturally impact its surrounding environment.
At an interrelational level, even though people wouldn't forcibly agree with one another, compassion would be predominant. We can't help but feel sympathy for anti-heroes, so the result would be the same reading about someone else's life. If everyone was able to take back control of his/her own narrative, the newly-created transparency could lead to more trust and understanding.
The current organizational structure would collapse. The rich range of ideas human nature is capable of would destroy the traditional narratives based on meaningless labels. Manichaeism would be hardly believable. Humanity would remain as the only common denominator. New schools of thought would naturally emerge, but they would be driven by lucid acts and ideas rather than mere emotions, and everyone would agree on common principles. We are all different, but we all need the same things. Clearly expressing them through writing, instead of merely delegating our thought leadership to government executives or similar middle(wo)men, would unify humankind.
The number of creators would increase at an exponential rate. The number of blogs, newsletters, and books would explode. We would need more curators and tools to aggregate all the knowledge and build upon one another's work.
There would be too many creators and not enough consumers. Too many offers, not enough demand.
A natural convergence of cultures and ideas would lead to an extreme case of homogenization.
Writing could exacerbate auto-destructive behaviors (the best ideas aren't always the most widespread ones).
The amount of crappy books/blogs/newsletters would undermine most educational attempts.
The number of sects and personality cults would explode, making philosophical suicide more dominant than it's ever been.