First of all, someone running full speed at you with a knife, good chance he will still reach you and stab you after you drew and shot your chambered round.
Second, while you all have so much faith in safety mechanisms. THEY DO and CAN fail. Once while carrying an unloaded, freshly cleaned weapon (no ammo chambered, none in the clip) from my cleaning desk to the safe, had a child (who 9 times out of 10 knew better but kids are kids), bolt around a corner with a die cast toy and run flat out into me. The toy struck the weapon on the left side of the action. The impact managed to hit the safety in a way that it disengaged, despite no impact on the trigger (it was guarded by my entire hand) the firing pin went off. This was a weapon in good order, actually has a gunsmith look at it afterwards cause it freaked me out. I have never before or since seen a gun behave in that manner. That would have come of small comfort going to this kids grave. Had this weapon been loaded and chambered it would have discharged. From the impact of the kid, may or may not have hit anyone.
When I am in highly congested areas, or areas with lots of kids, I find their safety is more important than losing 1-2 seconds (at most) in pulling the slide back. When I am in the wilderness, in my vehicle, in a neighborhood or a scenario where my threat level goes up, then yeah, it is chambered.
There are at least as many variables in life and situations as there are stars in the sky. If you think the act of having a round in the chamber gives you a full sense of security then you have the false sense of security. I have had the opportunity to go through many secure (and we are talking VERY secure) facilities. There is never a single line of defense. Personal defense is the same. There is situational awareness, person defense moves, knives, keys, and other tools.
IF you care to charge me with a knife, pulling my gun would not be my first line. My first line would be using your own inertia against you. Putting that much effort into the charge, I guarantee you, you will miss me, and get hurt in the process. You will not get right back up and before you do, you will hear the slide, and I will have my gun on you fully chambered.
Am I prepared for everything? Anyone who says yes to that is kidding themselves. Could there arise a situation where I would not have the hand to pull the slide back? Absolutely. I do find it interesting, in the thread with 90+ real life scenarios where folks used their weapons in some fashion, not one of those would be an area where why weapon would be unchambered. Not one of those would have actually been hurt or helped chambered or not.
So please, while i respect everyone's right to carry as they see fit, try to respect others as well. This is about personal choice, and while I commend those who share their opinions on why they would always be chambered and situations that they would ask you to consider, I would equally condemn those who insist those who would be ever be unchambered, have no idea how to use their weapons, or are less manly, or any nonsense.
That being said...game on guys.