Setting aside the "Law of Exigent Circumstances" (1) where to preserve innocent life (the area we are speaking of here) .. anything goes..
To effectively use a knife in most situations rendering the opponent "hors de combat" (2) may well require a great number seperate wounds to the assailant. Since exangination is what may be required to causes cessation of all hostilities... it would likely be an extra bloody mess.. All preserved and photgraphed in ""Living Color" and presented to a Grand Jury then a Jury made of of people few of whom have ever actually seen violent death. Who have not killed anything but bugs or maybe a mouse in a mouse trap. People who are highly unlikely to have ever even dressed out a deer.
Justifying self defense with a fiream to a jury is a hard enough given the nature of many prosecutors .. Self defense with a knife would be many orders of magnitude even more difficult regardless of the merit of ones actions.
America is just not a knife culture and in US there is a cultural bias against knife use as a weapon.
For example...
For a long time before California fell off a political cliff.. It was a Felony to be in possesion of a concealed knife longer than something like 3.75 in.. at the same time being in possession of a concealed firearm was in many circumstances a misdemeanor.. Since that was Legislative and signed into law. The bias is well demonstrated ... it has not diminished.
(1) "Exigent circumstances" :
Circumstances that justify a person to take one or more actions which under normal circumstances may be considered unlawful.
While the focus today is on exigent circumstances surrounding police application of the 4th Amendment.. The term actually surpasses that one particular application.
For example Mr Brown sees a fire approaching his rural home and or homes in the area.. He knows Farmer Smith down the road has a Tractor with a blade he could use to cut a fire break.. Farmer Smith is not around to ask permission to use the Tractor.. Mr Brown applying the doctrine of "Exigent Circumstances" breaks down the locked door to Farmer Smiths house finds the Tractor Keys.. Takes the Tractor and heads down the road to fight the fire with it.. .Even if Farmer Smith were to file charges against Mr Brown for "Breaking and entering" , Grand theft tractor" Mr Brown's would have a legal defense to his actions successful or not under the Doctrine of Exigent Circumstances. (I say he saves everyone's homes and Farmer Smith's Corn Crop as well.. yay)
(2)
Hors de combat definition: disabled or injured | Meaning, pronunciation, translations and examples in American English
www.collinsdictionary.com
"out of the
fight; disabled; no longer able to fight"
"Cult of the Dummy Cord"