More moral questions

OK. To follow how I got to this idea, you might have to use some inductive reasoning, but bear with me for a minute.

So, I came home tonight, to an empty house, and I had forgotten to leave a light on so the house wasn't dark when I got home. I'm in the middle of re-reading quite a scary murder mystery, and I was thinking about that as I walked into the dark house. Then, as I walked through the door, I could see my shadow, and thought someone was standing in the kitchen. Needless to say, I jumped about a mile. Then, as I walked around and turned on all the light, I was thinking what I would do if someone had been there (all those self defence and kick-boxing classes? Run like crap.)...which led, naturally to me being murdered.

Which led me to thinking about the whole abortion discussion. The dispute is essentially (yes, yes, simplistic) over whether a foetus is a human being, and therefore has the same 'right' to a life.

Which leads me to my next moral dilemma (Are you happy again Katy?). Is it ever OK to kill a person, and if it is, when?

I think all of us have it in use to kill someone intentionally. i think it's a question of how far you can be pushed. For some people the threshhold is low (I just guaranteed the FBI will be monitoring my site from now on). For most of us, it's so low it will never happen, because we won't ever be put in a situation where it will be tested. But I think that a mother who has watched her children be killed or raped, and someone has turned a knife on her, could potentially (and perhaps justifiably) kill her attacker, provided she actually physically could.

I don't think this is really a question you can ask in the abstract. I think it is a case of situational ethics. Is it OK in self defence (depending on the situation, probably yes)? Is it OK as punishment for a crime (no)? What about in war(probably not)? In what situation is it ok to take another persons life? What about as euthanasia (possibly)?

Or is it never right, it's just that sometimes it's less wrong. That killing a person who is trying to kill you is justifiable not cos it's right, but because there is no other option? So we can stomach killing soldiers killing others because it is in the name of something? And euthanasia? And where does that leave suicide?

So, y'all, (sorry, i've been reading too many american websites) when is it justifiable? Or, when is it less wrong?

Thoughts?