It would be the last resort to save my life or someone elses life and that would be if I happened to be unarmed or disarmed at the time, God forbid.
The only thing that happens in a knife fight is that both parties will get cut, stabbed or both. Unless you're the likes of Michael Janich or Chuck Norris or course.
I have never carried a knife with even a remote intent to use it as a weapon. And as far as weapons go, anyone with an imagination can probably scan their surroundings for a second or two and find several "things" that could be used as a weapon within reach in many cases.
The only people or entities who gain anything from the notion of a knife as a weapon are the same people or entities who want to control or outlaw knives to some degree or even completely.