Unlike many other girls, I enjoy quite a lot gore and bloody violence in movies and games. Nevertheless, I think mindless homicides in the real world are wrong because you could end lives which could enrich yours in some ways. I would never kill for anything in the world somebody who might be completing, let's say, my next favourite book or music album or videogame. Or somebody who helps his/her loved ones on a daily basis. Everybody is useful in their own ways.
While it's true that if you were a serial killer, and you happened to end somebody's life, you could actually prevent bigger tragedies (think about a murderer who kills a person that would've turned out to be a kamikaze in the next couple of years), I think that everybody deserves a chance to live and make the most out of it.