I've carried tip up and down for over twenty years, mostly liner or frame lock. The few that would open were extremely inexpensive. Tip up is problematic, if it does open, it leaves the edge exposed. Clips don't always retain a knife against the back of the pocket, regardless of the advice that it's safe. As a gun owner, you've heard the discussion that the Glock safety works fine, too. And yet, some of us prefer a manual safety locking the action no matter what - which Glock will also sell, too.
If you absolutely don't want to worry about the knife opening, it has to lock shut, which is a hassle. Carrying tip down solves the problem completely, if you do put your hand in the pocket, the motion will likely close the blade, as will pulling it out to use. The reason so many don't like it is the assumption it "deploys" slower, which means speed of draw might leave them in second place in a lethal encounter. The same argument crops up in guns, too, "that split second might mean life and death!" What gets left out of the conversation is why someone ignored all the clues they were already in a life and death confrontation for the last few minutes. It goes to the usual monkey dance of one guy trying to make his case promoting his self image, not the actual reality of a tactical situation.
You can carry tip up, down, or fixed, use whatever locking system you want, the quality makers all do a good job. Better to concentrate what blade and handle styles suit your use first, a knife is a tool most often and should be chosen for that above all. The self defense aspects mean very little if you already carry a firearm, and if you don't, the acquired skills of unarmed self defense are better to have than a knife. They are required to have before edged weapons training in most disciplines anyway. Just carrying a knife won't do much if you can't defend against an attacker.
Stick to a quality knife maker and pick one you like, carry it, and learn how to not cut yourself. The best method is to carrry a slip joint with no lock, it will bite you, but only if you use it wrong to begin with. That way you don't get in the habit of trusting a locking blade - they can and will fail, every one, given enough time and ingenuity.
