I"m going to be the voice of dissent here and say that no, dammit, posting something on the web does
not mean everyone can just take it and distribute it the way they want to. And the fact that it's fanfic has nothing to do with it.
They are my word, they are my works, they are mine to decide about. If I ever found one of my stories on an archive I did not give archiving permission to, I will be right pissed off. I think a distributing license is not that bad an idea, considering the many opinions on what an archiving permission entails, and the many people who still think they have a right to archive anything they want, regardless of the author's consent.
(This is a general rant. I know nothing about the whole MA situation, so i'm keeping quiet about that. This is just about archving permissions in general)
(Edit: I know it seems ridiculous to even forbid emailing a copy to one's friend, but I've seen more than a few cases where where that went horribly wrong. It's not all about ego.)