A question about the film 'Pay It Forward'

A question about the film 'Pay It Forward'. I know this story is also a book, but I haven't read the book, so I'm putting it here incase the book is different from the film.

Why do they kill off the protagonist at the end of this story? This is something I've never understood, and I am yet to figure out the reasoning for it. To me, there doesn't seem to be any reason to kill him.There's no moral underpinning that comes out of it and it's not like they needed to do it to prove a point about anything... It seems to simply be a shock value thing. I can't for the life of me figure out what the meaning is behind having him killed. He is killed trying to save his friend who is getting bullied, and the only message that seems to come out of that is "don't help people or you'll get killed". I'm assuming that's not what the message is meant to be though, or else it pretty much defeats the purpose of the whole film.

Anybody else have any better ideas than me?