I'm asking on a moral level.

If human lives are valuable, then I suppose the same also applies to my own life. If a hostile stranger appeared at night in my house, I would take his life to protect mine. Yes, the entire situation is regretful, but it was his choice to make it happen, not mine.

I wouldn't kill a person over stealing a candy from me, or trespassing on my lawn.

morality is subjective; there's no universal morality. That's why laws exist - to make clear what is acceptable to do, and what is not.