You cannot value life and still call murder justifiable (I'm going to assume you value life here.), who are you, or Anyone for that matter, to say what is punishable by death or not? Who are you to say what is right and what is wrong?
Most of Germany would have been bummed out about Hitlers death, I'm sure. But it seeming unjustified to them doesn't changed the fact that billions more would have applauded it. Hell, millions would have had no clue who Hitler was, and be largely apathetic had he died or not. It being unjustified to some, or hell, even the vast majority doesn't change the fact that nearly every murder is justified by some person or persons.
I think life does have value, but also that the value is based solely on your own perception of it.
Say a man does break into your home, sees you there. He is now forced to ask himself if your life is worth the chance of going to prison. Or if you're armed, he may even ask himself if your life measures up to his own. This is true on the flip side as well, you're also frightened, and asking yourself how much does this mans life measure up to your own?
If you did kill the robber, then calling it self defense would be a lie. You would have made a conscious decision to end his life, because you thought you where worth more than him. And why wouldn't you? You know every detail about yourself, your dreams, your ambitions. All you would likely know about him, is he's some scary guy invading your home and threatening your life.
We always judge lives as being worth more or less than our own, even at a subconscious level. That doesn't mean we have to like it, and that doesn't mean it's fair. But it does happen.
I'm not saying to go out and kill some guy you don't like because you think your better than him. We're capable of making choices and constructing and following our own moral guidelines for a reason. But rather when it comes to the question of "Do you sacrifice the life of One to save a Million" it's not a matter of arithmetic but rather who is being asked the question. Do you ask the One person to be sacrificed? Their father? Maybe one of the Million? How about a child out of the Million? Maybe ask someone aware of this proposed sacrifice, but not directly related? How about asking someone not even aware that it's going on?
People are killed every day, and you can't stop that. It's a scary thought, but anyone has the ability to become a killer given the right or wrong circumstances.
Sorry, I got to rambling there, I could go on, but I'm not even sure where I started off now.
Edit: Everything I covered here got covered better by the above posters, just read their stuff again.