IT'S A FUCKING VIDEO GAME. THEY ARE KILLING FUCKING ALIENS. THIS IS SCIENCE-FUCKING-FICTION.
There, I feel better. Now, on a more down-to-earth note, please allow me to ask this: How many books and/or movies have ever depicted violence in a church or other place of worship? Now, how many times in said books and/or movies was the violence, that was so graphically depicted, aimed at other human or human-like forms; how many times was it against aliens?
Food for thought.