Which film is this line from?

That is a quote from the German philosopher Friedrich Nietzsche. Maybe you can google that and find the movie. Sounds like something Stephen King might use??

Edit: Maybe a Harry Potter movie??

Dunno but I like it

TTH is correct that this line came from a German philosopher.

I was thinking that the line may have been used in a vampire movie. Characters that fight vampires sometimes get bitten and become a monster (vampire) themselves.

"W"

"W"

could you enlighten my considerable darkness as to your answer Lightwizard?

That is the Oliver Stone film about George W. Bush -- it fits, but that is, of course, not it! Did you try an IMDb search?