Johnny Blazes is mostly referring to those untrained in martial arts. I have seen them fight, and I have been in fights with people who were obviously not trained in any sort of fighting. I understand his point -
However, this does not necessarily make a non-martial artist ineffective with a knife. A knife is a deadly weapon in a manner that ones fists or feet really arent. Even a well trained and experienced martial artist would be hard pressed to deliver a fatal blow in combat with their bare hands. It can happen, but it's rare. People are tough to kill with your bare hands, regardless of your martial conditioning. With a good knife it only takes a small cut on a major artery at the neck, wrist, bicept, inner thigh, or even back of the hand, to kill you or incapacitate you. Maybe not instantly, but it makes it difficult to fight on, and if you die after killing your opponent, then what's the point?
Respect everyone with a weapon. I know I do.
When I fight with or without a weapon, I try to keep my opponent at a distance. I'm 6' tall, 200lbs, muscular, and a fearless Cherokee brave. I am trained in Tae Kwon Do, Ju Jutsu, Shotokan, Ken Jutsu, and some Bowie techniques. I have been in maybe 30-40 fights in my life - some with other Cherokees(we're just a bunch of trouble makers) and some with 'the white man', most of which seem to have issues with indians, or otherwise were would-be bullies. Most of my hand to hand fighting was before college.
More recently fights tended to include weapons either on my part or the attacker. In my experience, I would prefer to smack someone upside the head with a small stick, or simply point a gun and tell them to GET, than get into a wrestling match with them. My martial arts are a last resort. In all the fights I have been in, the ones where I came away the obvious victor tended to be when I was armed. Sometimes never having to strike a blow or fire a shot. Most bullies and criminals are cowards at heart. Displaying a weapon you are willing to use tends to defuse the situation in my experience. When Cherokees, and most Indians, fight you lose face if you have a better weapon. On the street, you can lose your life if you don't have the better weapon.
For self defense, I purposely carry only one lethal weapon; my Walther PPK. It is a last resort. Otherwise I stick with a lightweight aerospace aluminum baton from ASP that fits in my back pocket, and pepper spray(usually in a glove box, rarely carried). The baton can do a tremendous amount of damage to soft tissue, and it can easily break bones. Such attacks are rarely lethal, but can instantly stop a fight. A baton can kill if you hit the attacker in the head, though, as it does have a solid steel tip. All in all, it is a superior weapon to any knife unless your goal is to kill your opponent. I also feel it is a superior weapon to use against a knife. It has more reach, is just as fast into action, comes out of nowhere, and can easily smack a knife out of the hand, or break the hand or wrist or arm etc.
A knife is a lethal weapon along the lines of a gun - and most courts and D.A.'s view it as such. I do carry one(A Cold Steel Scimitar which recently replaced a Cuda Dominator), and I know I might have to go to it if the going gets rough. But I mostly have it as a utility knife and curio, not for defense. Maybe it's the old politically correct man in me, or maybe it's my Cherokee blood, but I prefer to beat an opponent without killing them. I nearly killed a man once hitting him with a 25# chain. I never felt any remorse as he instigated the attack and it was all I had handy, but I always thought it was overkill for the situation and took measures to correct it.
Basically speaking, when you don't leave a corpse or a graviously injured person, and can walk away from a fight unharmed, the entire episode it over. No cops asking questions, no law suits, no relatives looking for vengeance, etc. That's my preferred way to handle an attacker.
WYK