Our Mission is to "provide the structure, community, and encouragement to help people use their voices, achieve creative goals, and build new worlds—on and off the page." It is not our place to tell writers how to write, or to deem which approaches to writing are legitimate vs. illegitimate. Writers themselves must make conscientious personal decisions about their approaches to writing as a matter of their own free choice.
We are stating this in the wake of bullying and harassment that entered our spaces in the form of chastisements about "correct" and "legitimate" ways to write and acceptable vs. unacceptable writing tools. In the name of civility, mutual respect between writers, and inclusion, we don't want that type of virtue signaling in our spaces. Our priority is creating a welcoming environment for all writers.
This position extends to our partnerships with sponsors and affiliates, with authors who we invite to write pep talks or serve as camp counselors, and to people who we invite to participate in events. NaNoWriMo is a global community of more than 550,000 writers who we fully expect to have different values, different needs, different preferences, and different curiosities. Because Wrimos are not a monolith, we can't cater to a specific author archetype or ideology.
NaNoWriMo is a 25-year-old organization with staff that has been in the writing community for a very long time. We've seen tremendous harm done over the years by writers who choose to pick at others' methods. We've seen cases of indie authors delegitimized by traditionally published authors, we've seen certain genres (such as romance) dismissed as unserious; we've seen fanfiction writers shamed for everything from plagiarism to lack of originality; the list goes on.
Not only is this sort of shaming unnecessary and often mean. It's proven itself to be short-sighted. Some of the most shamed groups within the writing community are also the most successful (e.g., Romance is one of the highest-grossing genres; an increasing body of data shows that indie authors do better than trad-pub authors, and some of the biggest names in publishing started out in fanfic).
We fulfill our mission by supporting the humans doing the writing. That means not allowing judgmental dynamics to enter into our spaces.
Note: this statement was revised to clarify and contextualize these comments in the wake of questions about our motivation for speaking on this topic.