Say you're a vampire.
Your best friend dies in a car accident. You are with him. The drunk driver of the truck who hits you doesn't die.
You're badly hurt. There's only one way you can heal yourself. Your friend is dead. His blood will not help you.
Your best friend had a prophetic dream about the accident and his subsequent death. He did not tell you about the dream, or tell the rest of your friends.
He contacted his sister, who has the peculiar talent to bring the dead back to life, and asked for her help, fully knowing that her talent would require a life for a life.
Fully knowing that the driver of the truck would survive the initial accident.
He had no way to track this person down to turn him from this path. To save his own life as well as the driver's life. He knows what his sister would have to do to bring him back to life. He asks her to come anyway.
You are grieving. Hurting. Badly wounded. The driver manages to exit his smashed up vehicle and stagger onto the road.
You know nothing of the sister's talent, only that your friend had asked her for help.
You are a vampire. There's only one way for you to heal.
You don't remember what happens, only that when you're next aware, the driver is dead.
Later, you find out he would have died anyway to bring your friend back to life. Your friend's sister has no problems with this.
You've never killed someone before. In your right mind, you would not have killed someone to save your own life. But you were not in your right mind.
Your friend is now alive. The driver's body will never be found. No one will ever question you about this. Your friends do not damn you because of what you did. They do not turn away from you. No one thinks you are a monster--except, perhaps, for yourself.
Can you live with what you've done?