If you are going to carry a weapon, in many jurisdictions within CONUS, it doesn’t matter if it is a pistol, knife, or brass knuckles, all are illegal to carry concealed without a permit. (These laws vary widely, depending on blade length regulations, and so forth.) In fact, in some jurisdictions such as California, concealed carry of a “martial arts weapons” (Liberal oxymoron–aren’t weapons martial by definition?) is a felony, but having a Glock tucked into your waistband is a “Class A” misdemeanor [for the first offense.] Therefore, if you are going to carry, then why not carry something truly deadly (such as a pistol). Yes, a knife can be employed nearly instantaneously, but how many of us have actually seen a knife used with ill-intent? How about a machete? Nasty business, this is. You’d better have a solidly sorted spiritual point-of-origin on these matters.
As to a martial arts system that instructs the use of an artificial (non-organic) weapon as a primary source of combat, what happens when the novice loses his knife/stick/nunchaku? What then? Without the underlying principles of motion, the beginner is wolf-bait…any system of martial arts worth its salt will emphasize the principles of applied motion, as in Newtonian Physics. Any hand-held weapon should only enhance the attack, not substitute for it. Now projectile weaponry is another matter. Just my hard-won $2.83 worth (that’s $0.02, adjusted for inflation, before taxes) – Bonehedz