well, i don't think it was intended that the bad guys were eeeevil (the ambiguity of evil being relevant to the whole story). and the relationship twixt hellboy and liz is a gimme (set up in the first movie).

as for needing a big reason for humanity to live, i think you're digging way to too deep. love is worth keeping alive. they repeat it a hundred and fifty times.

just enjoy the shiny. i think you are totally over-thinking this one.