I'd venture to suggest that any knife is of limited use as a weapon, unless the user has been trained in its use as such. Certainly a 2" fruit knife will kill however, if stuck in the right place.
Conversely, a terrorist with a black belt in Kung Fu doesn't need one.
And anybody with a limp and a walking stick has a far more lethal weapon potentially. Similarly a partly metallic false leg will hide many things (anybody read Reach for the Sky ?).
A degree of commonsence would be appropriate I think.
Incidentally swiss army knives do set off the detectors at any BAA airport that I've been through, but I've been a few places (mostly Former Warsaw pact countries)where they don't.
G