I recently overheard an elder saying he can't wait to run a bulldozer in the new system and push all the dead bodies around....
It was a disgusting thing to hear.
So to answer your question, I think because of the whole "all wordly people will be destroyed at Armegeddon" belief, they discount the value of "worldly" people's lives.
Really, though, how could they not feel that way considering the belief system. In JW land, God is holding back his anger right now.
They believe that God is just chomping at the bits to destroy these people. So what's a few early casualties? No big deal.
But let something happen to a precious JW...oh it's time to wail and moan. I mean that's Gods people being hurt, not some worthless worldly person.
-Not many JWs can or will articulate their true level of disdain for their fellow man, but its just under the surface for many of them.