Note: major spoilers follow! (If that wasn't already clear from the title.)
I was having a discussion with someone yesterday about John Wyndham's novel The Midwich Cuckoos, specifically its ending, and we couldn't agree on the morality of the final act.
What is the moral of the story? When Zellaby sets the bomb to kill all the Children, is this an act of heroism or of murder? Is he ridding the village (and the planet) of a threat which would eventually have destroyed us, or is he killing dozens of sentient creatures just because they were superior to us?