I figured that letting people write without an account was not worth the added complexity, especially for a minimum viable product. You are free to look at any of the published wikis; the interface for writing a wiki looks almost exactly the same. I made the sign-up process as painless as possible, in case you ever change your mind.
No thanks. No matter how simple you make a sign-up process, it'll always turn people away.
That is not a fact.
It's not, it's speculation. But it's probably naive to assume it's possible to require information from a user (username, password is about minimal) and not turn at least somebody away.
Also, perhaps not impossible, but I've yet to see it.