The question we should ask ourselves is, if it's such a useless SD knife why did so many people carried one in the good old days before the onset of small handguns.
Yes it's a last ditch knife to defend your life with. Yes a pistol and o.c. spray are better self defense tools.
But Blackjacks, saps and push dagger where not carried and used because they where useless.
Now envision you live in an environment where you could need to defend your life with a knife and any knife would get you in trouble, where any self defense tool is illegal and firearms are not available to the general public let alone carrying one.
So defending yourself with anything will automatically get you in trouble with the law. Is the PD still a bad option if you carry a second small non locking knife as a EDC cutting tool?
Not everyone lives in the USA and has the option to carry a firearm or anything legal for self defense.
Most countries in Europe outlaw anything carried for self defense. Even pepperspray. What option do these people have?