By the same token, you can carry a wrench in places where you can't carry a gun or knife. Personally I prefer blunt implements for self defense in most circumstances (non-military). They can be just as effective, require less expertise, and are less likely to get you in trouble than cutting the throat of a common, garden-variety mugger, no matter how much he might deserve it. As for walking around with various types of weapons, it's my understanding that even in open-carry states (for firearms) there are usually pretty severe restrictions on large, edged weapons.
I enjoy these discussions as much as anyone, but let's face it, mostly it's comparing apples and oranges. You don't want to bring a knife to a gun fight. You don't want use a pocket knife against a man with a khukuri. An actual duel between two people armed with comparable fixed blade knives is one of the least likely scenarios in the life of an ordinary citizen, rather on a par with having to face down a lion that just escaped from the zoo. I'd bet on the lion, no matter what kind of blade you might be carrying in anticipation of that confrontation.