Now, the checkbox for crossposting was NOT grayed out- I was able to tell LJ to send it to Facebook. I told it to crosspost a comment on a friends-locked LJ entry- and it did not appear on my Facebook.
Either there's a great deal of shrieking going on about something untrue (not that that ever happens on LJ), or LJ is working EVEN WORSE THAN USUAL at accomplishing something they intended to. In future, I would suggest that people test things before they jump to a worst-case-scenario conclusion about what has happened.
Yes, Chicken Little, the LJ isn't falling.