Rest assured I won't click that "cross-post to Facebook/Twitter" box on any comments I make on your posts.
And while I do have my LJ posts showing up on FB (and have for several months now), it's actually fed the other direction: namely, I have FB check for new public entries (it won't catch friends-locked ones) and put them up as notes. It only posts my entry; not your comments.
I have a permanent LJ account, so fleeing elsewhere wouldn't make much sense, although I still could someday. Anyway, I've long since left behind the notion of using LJ as my main source of drama and personal confession, and use it more as my Authorial Blog. (I'm not fond of self-promotion, but they tell us we have to do it.) So, honestly, I don't care much if you pingback my entries or cross-post your remarks upon them, except in the rare event of my locked and obviously sensitive-material posts.
But, again, I won't do that to you, since that is obviously not what most people wish to see done with their posts.
Chances are LJ will scramble to fix that brilliant little idea quite soon here, given the uproar...