My father always had an old slipjoint or other in his pocket. He was blue-collar and really worked the heck out of his knives. My first knife was a very worn-down Camillus scout knife with the main blade all rusted and sharpened almost down to a splinter.
For years I carried all types of slips, including Schrade, Buck, Camillus, Case, Victorinox, and Wenger. Currently I virtually always have 2 slipjoints on me, the Victorinox Soldier and Vic Executive. The Executive is my light-duty grooming, package-opening, etc., knife. My Soldier is for heavier-duty use, and both get used on a daily basis.
I also carry some type of one-hander, often my CRK Seb, or a Spyderco Endura or Delica.
I tend to use the SAKs the most every day. I have had instances where the one-handers were invaluable, and their performance is magnificent. But the slips work outstanding as well, and they do not draw the attention that the one-handers do. I like having the choice, but truth be told, before I got my first one-hander in '97, I carried only one slipjoint SAK or other pocketknife(s) and never had any problems. I've also heard of some guys using their expensive one-hand tactical to open cans of food; but I can do that very easily with my $20 Vic Soldier, do it more cleanly, and without any risk at all of damage to an expensive blade.
IMO, not enough people carry knives as normal utility tools in society anyway. It's looked down upon by most people nowadays. So if you carry and use your knives, more power to you, regardless of whether it's tactical or slipjoint. I'll take both; for me, each had its time and purpose!
Jim