I don't think it was any accident of fate that in the old days, the lock blade never was very popular among working class like the jacks. Plain old slip joints were the rule of the day. The barlow was certain one of the kings, and there were teardrop jacks, harness jacks, sleaveboard jacks, and many more. They had lock backs around. They had them in the 1800's.
I'm not so sure. This could be a matter of economic cost and local culture. My understanding of the history of the Spanish Navaja was that it was commonly carried in that culture in that time. My understanding is also that a part of the appeal of the Navaja was it's dual use as working knife and concealed weapon. We should not sanitize the popularity of the Buck 110, or current EMT/tactical knives in the same way. Sales of the Buck 110 were as much driven by biker gangs and the military as they were workers. The Spyderco knife made a huge hit among EMTs who could justify a knife for rescue but who not allowed to carry guns. Useful to have a scary looking weapon when entering a situation before police back up. And the general US market is definitely marked with larger concerns of self-defense and concealed weapons. Just look at the pop up adds on this site.
Regarding the cost issue, my understanding of the etymology of the term "jackknife" is that it is related to the older English term "jackleg" - referring to low wage workers who could only afford inexpensive in adequate tools leading to shoddy work. Jackleg meant, roughly shoddy or crooked or untrustworthy.
Most of the old catalogues had tons of jacks, but relatively few locking blade knives. But they had "hunting" knives.
I think a part of the larger US cultural shift towards city life is a general disfavor of fixed blade knives. I suspect it goes even deeper in the US and suspect that every day carry of fixed blades disappeared from EDC use as agricultural culture displaced frontier culture during the expansion westward. Hence, fixed blades became synonymous with "hunting knife" for a while and folding knives like cowboy knives and sodbusters appeared.
I won't argue that a good lock on a blade makes the knife safer. Of course it does. But...I think if one is introduced to knives with a lock blade, and never has to learn good knife handling habits, that person is at a disadvantage, and even may be an accident waiting to happen if something fails. A little wear on the corner of a locking bar, a little lint in the notch, anything, and you have a lock that will fail.
These are all really good points. One thing I keep in mind is that different designs fail in different ways. It's practically impossible for a collar lock (like Opinel) to fail catastrophically short of breaking the knife outright. They *CAN* fail with warning if the lock ring begins to creep around to the open position. In contrast, both lockbacks and liner/frame locks can fail catastrophically with little or no warning. In terms of general robustness and safety, I rate the designs as follows:
1) collar locks (e.g. Opinel)
2) lockback (e.g. Buck)
3) Liner/frame locks (e.g everybody and their uncle)
My beef with liner locks is my tendency to bump them.
But there is just no way, any lock on a knife, is going to put it anywhere in the neighborhood of being as safe as a fixed blade. No way. If someone is concerned about a knife folding, then just stay away from a folding knife. But if all you want is a cutting tool for the pocket, and not a staying, prying, poking, zombie slaying wonder blade, then a slip joint pocket knife is fine. There must be a reason they have been popular for hundreds of years.
I think this is a bit overstated as an either or.
I group my use of knives into 3, not 2 groups.
LIGHT, SIMPLE CUTTING - a slip joint or friction folder is fine for this and often preferred owing to the fast open/fast close. I often use my Opinels without the lock engaged for this reason.
STABBING, PRYING, CHOPPING - This is hard work that I'll only attempt with a fixed blade. I totally disagree with the assertion that knives shouldn't get used as a prying tool, btw. So did/does the Army, hence the design of the Ka-Bar. It's a utility tool.
HARD USE - This includes cutting out sapplings, clearing out gardens, working in my shop, cutting down boxes. In this case, I know better than to abuse the knife as a pry bar because it's a folder. But, I'm also working long enough and hard enough that I might get sloppy and
bump a blade hard enough to close a non-locking knife. This often happens when cutting out brush. I get the blade stuck and twist it a bit to get it out. Dangerous with a slip joint, not so abusive that will cause a locker to fail. In this mode, locking knives are safer, at least to my mind.
), they forbid their use. 
:thumbdn:
