Slip joints . . . I don't know . . . jury's out on that one. I have had slipies open in my pocket but mostly because I have been unconsciously pinching them open and closed while I talked to some one etc. Yah that's a wake up call the first time it is sticking through your pocket and the more you try to disengage it the more it opens. I finally had to just stop doing that.
If "the jury is still out on that one" they have been out since the first Barlow's went into production in the
1600's.
The verdict has been in for hundreds of years. Barring a broken spring, or excessive wear at the spring and tang, a slipjoint will not, and cannot, "fall open" in your pocket.
I have carried a multi-blade slipjoint in my pocket for over 55 years. I've never had a blade open in my pocket. Keep in mind, the knife in question was not always new. Some were and are well over 100 to 150 years old.
My father carried a slipjoint from the time he was 6 or 7, until the day he died, a few months before his 83'd birthday. He never had a knife fall open in his pocket. Ditto for his dad (although he died young, at age 53. He got his first knife between 6 and 10.)
My great-great grandfather on my mother's side carried a slipjoint from 1897 or so until he died in 1973. He never had a kinfe fall open in his pocket. (as a matter of fact, he still has one in his pocket. He requested he be buried with his favorite pocketknife, which was an anniversary present from his wife, in the 1940's. (she passed in 1963)
Barring excessive wear or mechanical failure, I have never heard of a slipjoint "falling open" or opening in anyone's pocket, be the knife a cheap no-name sub-$1.00 gas station/service station special to an expensive name brand knife.
And yes, I have read Nessmuk and Kephart, both of whom used their slipjoints in "bushcraft" (they also used a 4 to 5 inch fixed blade, and never once batoned either of their knives). They never mention a pocketknife opening in their pockets, either.
(also, if you use a slipjoint for cutting, and not prying stabbing, or sawing, the blade cannot close on your finger(s), either. The forces applied to the blade when cutting force the blade
open unless you're doing something stupid.)
Based upon your comments and claims of a slipjoint opening in your pocket, I suspect you have never owned one, and probably have ever even held one.
Before you start spweing falsehoods on how "unsafe" they are, based on lies told over the Internet, and urban legend, why not spend $8 to $12 and buy yourself a Rough Rider slipjoint and try them?
I have no problem with your preference for a one hand opening "modern". They are not my cup of tea, but I have no reason to demonize them to justify my preference for a traditional. Why do (some, not all) users of the "modern" knives feel the need to justify their choice by demonizing the single or multi-blade traditional slipjoint knife?