I can turn off posting to Facebook if I post to LJ separately. But if the LJ post comes through as an auto-post from DW, I can't turn off the relay to FB manually because I didn't make the post manually and it's already created, if that makes any sense.

Kat's suggestion fixes the problem of the DW->LJ posts defaulting to public... except that I've just realized that means none of my LJ posts will go to Facebook now, even the ones I'd like to. *headdesk*

So I guess I'm just going to have to go on posting fannish stuff here, where it will go to LJ as a locked post by default, and writing stuff over on LJ, where it can flow through to Facebook as it otter. But then I'll have to come back here and manually repost the LJ-first stuff. Meh.