Except if you think about MLK's life you'd think "What the hell context would this have been in? Who is this dead 'enemy' who killed 'thousands'?"
The (fake) quote does come across to me as a bit too holier-than-thou. It's a form of cost-free conspicuous po-facedness to which you set your facebook status to mark yourself as being morally superior to the less sophisticated USA-USA chanting crowd. It doesn't sound like the kind of thing MLK would have said, because MLK wasn't all that into "Hey look I'm better than you" type announcements.
There's a scene in Return of the Jedi where the Super Star Destroyer crashes into the Death Star. Everybody else on the bridge cheers, but Admiral Ackbar looks sad and bows his head, acknowleding the awfulness of the loss of life even if they were evil enemies who were trying to kill everyone. The listed quote is propagated by Ackbar wannabees with a George Lucas level view of what being morally sophisticated looks like.