enoughisenough: I never believed that only JWs would be spared at Armageddon.
I think that many of us figured that lots of non-JWs would make it for any number of reasons (not getting preached to, for example). But also, we could justify the belief because we felt like God could do anything and it would be okay. We believed that God could kill anyone at any time without a reason because He had given us life, so He could take it back and that was okay, that we should be grateful that we were able to live at all. And so on.
Thus, the idea that God would massacre billions of people in order to save a few million didn't really sound as horrifying as it should have, because it was okay- God was doing it, and He was incapable of doing anything bad.