I carry at least two knives on my person at all times. My primary blade is a Camillus Heat; its little under four inches. My "primary blade retention tool" aka "backup knife" is a Cold Steel Vaquero Grande (6 inch blade). And you ask, would I be willing to stab someone to defend my own life? My answer to your question is, you bet and I've came pretty close.
I was walking down a street just around my block. Two gang-member type guys noticed me, one of them wanted to steal my hat (he whispered his intent to his friend, I just overheard). As he came near me he started saying, "hey what’s up man. That’s a nice hat you know, let me check it out" while grabbing his crouch. His shirt lifted up enough for me to see that he had a belt push-knife. When the guy was a little over an arms length away he touched his knife right about to pull it out. My hand had been in my pocket ever since I first seen these guys but when I seen the glint of his metal, I took mine out and made a swipe towards his face and then took a few steps back.
I barely scratched the guy's upper neck. Not enough for blood and it didn't even turn red – was only white scratch. I was holding a cheap $7 knife that wasn't very sharp. But it was enough to scare the crap out of this guy. The other guy just stood there in shock looking at his friend's neck, telling him not to worry and that he didn't see any blood. We all must have just stood there for a good 15-20 seconds not saying anything and not moving. Neither one of us wanted to provoke the other. Eventually he was just like, "hey I was just f*ing around, be cool 'ight" and I told him I wasn't letting him walk away with his knife. -- My worry was that if I walk away he could always come after me from behind. -- He paused for a few seconds, dropped the knife on the floor and then both guys just walked away.
I think what happened was, these guys thought they were real bad asses and I looked like an easy target. Then all of a sudden without warning they found themselves as the targets.
I'm glade I didn't stab the guy or seriously injure him. I'm also glade I didn't run away like a coward and that I didn't end up spending a night in jail waiting for a judge to decide if I was in the right or wrong. I ditched that little knife and replaced it with what I carry now. My view now is that just presenting a knife and showing a willingness to use it on your attacker (soon to be victim) can stop the incident right there.
The gold knife in the first picture is the one I carried. The Push knife in the second photo is the knife the guy dropped. I kepted it as a little reminder...well okay I kepted it as a little trophy - but is that really so wrong?