Knives are not good defensive tools, period. Certainly they can be used for defense. So can an ink pen.
What bothers me about these posts is that many people feel they could actually use a knife effectively for defense. These are usually the same people who espouse that carrying any gun under .40 cal will get you killed.
A knife is a poor choice for defense compared to a .25 automatic.
I would agree with your last statement. Nearly any gun is better than a knife, and I am not one to say anything less than a .40 is zero. But in the post I was commenting about, you didn't compare a knife to a mousegun, you compared it to a screwdriver. That is where we disagree.
I would agree that it is bothersome when people think owning a knife makes them an expert in knife defensive tactics, but the same could be said about owning a screwdriver! My point is that for the same amount of training, I would rather have a good sturdy knife to defend myself than a screwdriver, but I would still take a gun over either.