I've tried to not chime in on this, but I'm just so darn opinionated...
No matter how "prepared" someone is, I don't imagine it would be easy to get over taking someone's life. Additionally, if you believe in a creator, you have to imagine you'll have some accountability for taking that life. I'll speak in a Christian context as that's what I know. Taking an intruders life may save my life for a time, but I've incurred "bloodguilt". I could lose my everlasting life for that. However, if that intruder takes my life after I passed up the "opportunity" to kill him, I'll be resurrected and he'll have to face whatever judgement awaits him. I'll take my chances with the latter.
If you don't believe in a Creator I understand that you don't believe in that same accountability. You have to justify your choices with yourself and whatever your beliefs are. I just sincerely hope none of you ever have to make that choice.
All of this being said, I couldn't say what I would do if a close member of my family or a close friend were in mortal danger. However, I'm not going to put myself in a position to make a rash, poor decision by having a lethal weapon loaded and ready to go.
Finally, I don't judge anyone for their beliefs. I don't expect others to be guided or judged based on my opinions. However, if you're a Christian, or claim to be, it's at least something to think about.