Imagine the profound impact a movie like "I am Legend" would have had if they'd stuck to the original ending. What's more frightening is to imagine the reason they changed it at all.

"I don't like this ending where it turns out the zombies aren't bad guys. Takes too much thinking. I know! Let's throw in god and fate instead! People like that stuff. Let's keep all the foreshadowing that suggests the zombies aren't bad, though. Lord knows smart people need to stay on their toes."

-Quip